Acoustic orthopedic tracking system and methods

ABSTRACT

Systems, devices, and methods are disclosed for acquiring and providing information about orthopedic features of a body using acoustic energy. In some aspects, an acoustic orthopedic tracking system includes portable acoustic transducers to obtain orthopedic position information for feeding the information to an orthopedic surgical system for surgical operations.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent document is a Divisional of U.S. Nonprovisional patentapplication Ser. No. 15/289,013, filed Oct. 7, 2016, which claims thebenefit of U.S. Provisional Patent Application No. 62/239,169, filedOct. 8, 2015. The entire content of the before-mentioned patentapplication is incorporated by reference as part of the disclosure ofthis application.

TECHNICAL FIELD

This patent document relates to systems, devices, and processes that useacoustic energy for diagnostics and therapy.

BACKGROUND

Acoustic imaging is an imaging modality that employs the properties ofsound waves traveling through a medium to render a visual image. Highfrequency acoustic imaging has been used as an imaging modality fordecades in a variety of biomedical fields to view internal structuresand functions of animals and humans. High frequency acoustic waves usedin biomedical imaging may operate in different frequencies, e.g.,between 1 and 20 MHz, or even higher frequencies, and are often termedultrasound waves. Fundamentally, ultrasound imaging operates the sameprinciple as sound navigation and ranging (SONAR) in which atransmission of one or more acoustic waves results in one or more echoesfrom structures that are received and processed to form an image. Somefactors, including inadequate spatial resolution and tissuedifferentiation, can lead to less than desirable image quality usingconventional techniques of ultrasound imaging, which can limit its usefor many clinical indications or applications. Compared to other imagingmodalities, the real-time, non-ionizing, portable, and relativelylow-cost features of ultrasound imaging make it attractive forbiomedical applications.

SUMMARY

Systems, devices, and methods are disclosed for acquiring and providinginformation about orthopedic features of a body using acoustic energy.In some aspects, an acoustic orthopedic tracking system includesportable acoustic transducers to obtain orthopedic position informationfor feeding the information to an orthopedic surgical system forsurgical operations.

In some aspects of the present technology, an acoustic orthopedictracking system (OTS) includes an engineered acoustic array andsupporting structure, in which the acoustic array provides an acousticcoupling medium as it relates to the transducer structure and the bodypart of interest. For example, a plurality of ultrasound transducers ofthe acoustic array structure transmit and receive ultrasound waves thatare used to track the shape, location, and movement of bone inreal-time. The received ultrasound echoes are processed to estimate thesix degrees of freedom (6DoF) location coordinates of the bone, which insome implementations may be combined with 3D tomographic imaginginformation. Information provided by the acoustic OTS may be used inmedical treatment planning, medical procedures, surgical procedures,fully automated surgery, surgery assisted by robots, and biometrics.

In some aspects, a method for orthopedic tracking includes transmittingultrasound pulses from a plurality of ultrasound transducers, e.g.,sequentially one-at-a-time, simultaneously, or in a time-staggered ortime-delayed pattern. Each transmission is accompanied by receptions ofacoustic echoes on one or more transducer elements corresponding to asingle transmission. The received echoes are amplified, filtered, andtemporally sampled sufficiently to retain all relevant spectralinformation corresponding to the echoes from soft tissue and bone as isdictated by the Nyquist sampling theorem. Received echoes are digitallysampled and stored for processing. In some embodiments, the waveformsused include spread-spectrum waveforms, which are highly robustwaveforms to deleterious factors such as frequency and depth-dependentattenuation, electronic noise, cross-talk between adjacent channels, andacoustic reverberation. Due to the specular nature of bone reflections,echoes from the tissue-bone interface will present a different andidentifiable echo signature compared to echoes from soft tissue and fromwithin the bone itself. All bones, for example, the femur and tibia,have unique cross-sectional patterns over the length of the bone. Thespecular acoustic echo pattern from bone sampled at one or more pointson the bone are matched to a library of patterns sampled according tothe array geometry to determine the topography of the bone, and thus,estimate the orientation of the bone in 6DoF coordinate space accordingto the location of the transducers relative to a fixed point in space.Signal processing is applied to the amplitude and phase informationpresent in the received radio-frequency (RF) echoes to determine apattern match and identify 6DoF coordinates of the bone being tracked,estimates of the tissue and bone velocity and acceleration along theaxis of each transducer, as well parameters associated with the patternmatch, and estimates of the uncertainty in the identified 6DoFcoordinates.

In some applications, for example, the present technology can be used totrack the tibia and femur bones in the leg during computer assistedsurgery (CAS) of the knee, including, but not limited to, total kneearthroplasty (TKA) and total knee replacement (TKR). Currentstate-of-the-art TKA and TKR procedures require surgical placement of analignment rod into both the tibia and femur for rigidly tracking bothbones using external optical trackers. For example, to place thealignment rod, a small incision is made in the skin, a hole is drilledinto the bone, and the rod is screwed into the hole. The procedure isinvasive, resulting in unsightly scarring on the skin. It potentiallycompromises the integrity of the bone, particularly for elderlypatients. It is a site of potential infection, which can lead topost-surgical complications. The disclosed technology is envisioned toreplace this invasive tracking with non-invasive tracking.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a diagram of an exemplary acoustic orthopedic trackingsystem (OTS) of the present technology including an acoustic transducerarray and supporting structure used for acquiring acoustic imaging data.

FIG. 1B shows an image of an example acoustic OTS.

FIG. 1C shows a block diagram of an example embodiment of an acousticOTS implemented in conjunction with an external device or system.

FIG. 1D shows a block diagram of an example embodiment of the dataprocessing unit.

FIG. 1E shows an example synthetic aperture ultrasound/acoustic (SAU)system.

FIG. 2A shows a schematic of an exemplary acoustic transducer arraystructure of the present technology, showing top, side andcross-sectional views of the structure.

FIG. 2B shows a diagram of the exemplary acoustic transducer arraystructure, including an acoustic coupler to interface with a receivingbody for acoustic signal transmission and reception.

FIG. 3A shows various three dimensional views of the acoustic OTS 100attached to the femur of a subject.

FIG. 3B is another view of components shown in FIG. 3A.

FIG. 3C shows a three-dimensional view of a portion of the disclosedsystem employing two arrays of transducers per leg.

FIG. 3D is a three-dimensional view of a break-out diagram depicting theexample acoustic OTS 100 and the acoustic coupler 112 with respect tothe subject.

FIG. 4 shows a trade study diagram to explore element diameters andcenter frequencies that can be used for a particular set of constraintsfor an example acoustic OTS.

FIG. 5A shows a top view of an example tomographic array.

FIG. 5B shows a top view of an example tomographic array having specificparameters.

FIG. 5C shows a side view of the tomographic array of FIG. 5B.

FIG. 5D shows an isometric view of the tomographic array of FIG. 5B.

FIG. 5E shows an example tomographic array in which transmission isenabled on a contiguous group of elements.

FIG. 5F shows an example tomographic array in which the focal point ofthe beam falls within the sector subtended by the arc length and anglespanned by contiguous array elements.

FIG. 5G shows a second beam transmission in the tomographic array ofFIG. 5F.

FIG. 5H shows an example configuration of a tomographic array in whichreceive aperture includes one or more elements centered or approximatelycentered with the transmit aperture.

FIG. 5I shows an example configuration of a tomographic array in whichf-number of 1 is maintained for two focal points.

FIG. 5J shows an example configuration of a tomographic array in whichmultiple transmissions are staggered in time.

FIG. 5K shows an example sequence of transmit and receive signals as afunction of time associated with the configuration in FIG. 5J.

FIG. 5L shows an example configuration of a tomographic array in whichone or more receptions occur on array elements that are between 90degrees and −90 degrees away from the phase center of the transmittingaperture.

FIG. 6A shows a specular echo signature from a human femur bonesuspended in water.

FIG. 6B is a specular echo signature showing patterns that match and donot match the specular component of the ultrasound echoes.

FIG. 7A shows an example radial patterns for a human femur.

FIG. 7B shows another view of radial patterns for a human femur.

FIG. 7C shows an example radial pattern for a human tibia.

FIG. 7D shows the circumference or perimeter as a function of length fora femur.

FIG. 7E shows the circumference or perimeter as a function of length fora tibia.

FIG. 8A shows a simple arrangement of two transducers transmitting andreceiving echoes though soft tissue that contains a bone.

FIG. 8B shows an example objective function associated with eachtransducer or beam or collection of transducers of collections of beams.

FIG. 9 shows an example system in which the acoustic OTS system isintegrated with a third party surgical navigation system (3PSNS).

FIG. 10A shows the relationship between the patient's bone coordinatesystem, the OTS ultrasound transducer array coordinate system and the3PSNS optical array coordinate system.

FIG. 10B illustrates a bone tracking coordinate system similar to FIG.10A but showing ultrasound array displacement at future time t=T.

FIG. 11 shows an example hardware block diagram for the OTS.

FIG. 12 shows a block diagram of an example OTS software architecture.

FIG. 13 shows a Femur six degrees of freedom (6DoF) coordinate system attime T.

DETAILED DESCRIPTION

Acoustic imaging can be performed by emitting an acoustic waveform(e.g., pulse) within a physical elastic medium, such as a biologicalmedium, including tissue. The acoustic waveform is transmitted from atransducer element (e.g., of an array of transducer elements) toward atarget volume of interest (VOI). Propagation of the acoustic waveform inthe medium toward the target volume can encounter structures that causethe acoustic waveform to become partly reflected from a boundary betweentwo mediums (e.g., differing biological tissue structures) and partiallytransmitted. The reflection of the transmitted acoustic waveform candepend on the acoustic impedance difference between the two mediums(e.g., at the interface between two different biological tissue types).For example, some of the acoustic energy of the transmitted acousticwaveform can be scattered back to the transducer at the interface to bereceived, and processed to extract information, while the remainder maytravel on and to the next medium. In some instances, scattering of thereflection may occur as the result of two or more impedances containedin the reflective medium acting as a scattering center. Additionally,for example, the acoustic energy can be refracted, diffracted, delayed,and/or attenuated based on the properties of the medium and/or thenature of the acoustic wave.

Acoustic imaging system transducers may employ an array of piezoelectricelements to transmit an acoustic pulse toward the target VOI (e.g.,target biological tissue) and receive the returned acoustic signals(echoes) that return from scattering structures within. In such systems,the transducer array functions as the aperture of the imaging system.The acoustic waveforms (e.g., ultrasound pulses) can be electronicallysteered and focused through a plane or volume and used to produce a 1D,2D and/or 3D map of the returned echoes used to form an image of thetarget. Beamforming can occur both in transmit and receive. In transmit,for example, beamforming can include the utilization of phasedifferences between channels to form, focus and steer the beam. In someimplementations, the ultrasound pulse and the returned echoestransmitted and received at the transducer array can be individuallydelayed in time at each transducer of the array to act as a phasedarray.

For example, acoustic wave speed and acoustic impedance differences canexist at the interface between the transducer and the medium to receivethe acoustic waveform, e.g., referred to as the receiving medium, forpropagation of the acoustic waveform toward the target volume. Thesedifferences disrupt the transmission of the acoustic signal andreception of the returned echoes, diminishing the quality of results orability to perform acoustic imaging, range-Doppler measurement, ortherapeutic applications. Acoustic impedance differences are caused bydiffering material properties (e.g., material density) of the twomediums and the acoustic wave velocity, such that a substantial amountof the emitted acoustic energy will be reflected at the interface,rather than transmitted in full across the interface.

In conventional real aperture ultrasound imaging systems, the quality ofimages directly depends on the acoustic field generated by thetransducer of the ultrasound system, and the image is typically acquiredsequentially, one axial image line at a time (i.e., scan of the targetarea range slice by slice). This sets limits on the frame rate duringimaging that may be detrimental in a variety of real-time ultrasoundimaging applications, e.g., including the imaging of moving targets.

To address limitations with conventional real aperture ultrasoundimaging, synthetic aperture ultrasound imaging can be used to improvethe quality of ultrasound images. A “synthetic aperture” is the conceptin which the successive use of one or more smaller, real apertures(sub-apertures) to examine a VOI, whose phase centers are moved along aknown one-dimensional (1D), two-dimensional (2D), and/orthree-dimensional (3D) path of a particular or arbitrary shape, torealize a larger effective (non-real) aperture for acquiring an image.The synthetic aperture can be formed by mechanically altering thespatial position of the electro-acoustic transducer (e.g., transducerarray) to the successive beam transmission and/or receiving locations,by electronically altering the phase center of the successive beamtransmission and/or receiving locations on the electro-acoustictransducer array, or by a combination of any of above. Syntheticaperture-based imaging was originally used in radar systems to imagelarge areas on the ground from aircraft scanning the area of interestfrom above. Synthetic aperture focusing in ultrasound imaging is basedon the geometric distance from the ultrasound transmitting elements tothe VOI location and the distance from that location back to theultrasound receiving element. In ultrasound imaging, the use of thesynthetic aperture enables the focusing on a point in the target regionby analyzing the received amplitude and phase data of the returnedechoes (e.g., mono-static and bi-static echoes), recorded at each of aplurality of transmitter and receiver positions from all directions, toprovide information about the entire area. Since the direction of thereturned echoes cannot be determined from one receiver channel alone,many receiver channels are used to determine the information containedin the returning echoes, which are processed across some or all of thechannels to ultimately render information used to produce the image ofthe target region.

The disclosed systems, devices, and methods for acoustic orthopedictracking may also include techniques for synthetic aperture acousticimaging and/or range-Doppler measurements. In some implementations, thedisclosed technology includes an architecture designed for generating,transmitting, receiving, and processing coherent, spread-spectrum,instantaneous-wideband, coded waveforms in synthetic aperture ultrasound(SAU) applications. Examples of such pertaining to the generation,transmission and data processing of coherent, spread-spectrum,instantaneous-wideband, coded waveforms and synthetic apertureultrasound are described in the U.S. Pat. No. 8,939,909 and U.S. PatentApplication Publication No. 2015/0080725, which are incorporated byreference as part of this patent document.

For example, the use of coherent waveforms in implementations of the SAUsystems can permit the complex correlation of a portion of, or theentire, echo return with a selected reference signal, such as, forexample, the transmitted waveform. Such coherent complex correlationspermit the reduction of image and signal artifacts and the extraction ofdata at lower signal-to-noise ratios and in the presence ofinterference.

The use of spread-spectrum signals in implementations of the SAU systemscan allow the definitive design of acoustic waveforms that havedeliberate and explicit amplitude and phase frequency content. Forexample, by explicitly defining the amplitude and/or phase of eachfrequency component of the spread-spectrum composite acoustic waveformscan be constructed such that signal and information processingtechniques can be employed to extract the maximal amount of informationfrom the echo returns, e.g., approaching mathematical limits.

The use of instantaneous coherent, wideband, spread-spectrum, codedwaveforms in implementations of the SAU systems can enable the captureof all available information during each transmit-receive interval,e.g., thereby minimizing the corruption of the returned signal by theinhomogeneous, dynamic nature of living biological specimens, and bymotion induced artifacts of the collection process. Additionally, forexample, fundamental physical parameters (e.g., such as bulk modulus,density, attenuation, acoustic impedance, amplitude reflections, groupdelay, or other) can be extracted by using signal and informationprocessing methods of the disclosed technology to enable differentiationand classification of the tissue in the VOI. For example, some signaland information processing methods of the disclosed SAU technology mayinclude inverse mathematical techniques operating on the receivedfrequency and angular dependent wideband, spread-spectrum, syntheticaperture received signal echoes for differentiating and/or classifyingtissue in the VOI, as well as expert system techniques, e.g.,deterministic, support vector network and neural network techniques.

Explicit amplitude and/or phase coding of each frequency component ofwaveforms in implementations of the disclosed SAU systems can providemultiple benefits. For example, amplitude coding allows for the explicitcompensation of the frequency-dispersive properties of the transducerarray and of the acoustic propagation channel. The amplitude and/orphase coding of each frequency component permits deterministicbeamforming and steering of wide-instantaneous waveforms. Explicitamplitude and phase coding of each frequency component of an exemplarytransmitted signal permits the minimization of the peak-to-average powerratio (PAPR), and the spreading of the acoustic power over a wide band,e.g., to minimize deleterious biological effects. For example, byexplicitly defining the amplitude and/or phase of each frequencycomponent of spread-spectrum signals, waveforms can be constructed thatmay be transmitted simultaneously, which exhibit minimal interferencewith each other, such that signal and information processing techniquescan be employed to recover the received signal associated with eachindividual transmitted waveform. Further, the coded, spread-spectrumacoustic waveforms of the disclosed SAU technology can allow for motioncompensation due to particular ambiguity properties of these waveforms.

Systems, devices, and methods are disclosed for acquiring and providinginformation about orthopedic features of a body using acoustic energy.In some aspects, an acoustic orthopedic tracking system includesportable device including an acoustic transducer array that conforms tothe subject's body part to obtain orthopedic position information and asignal and data processing unit to produce a data set identifying shape,location, and movement information of bone, e.g., for feeding theinformation in real-time to an external device for a diagnostic ortherapeutic application, e.g., such as an orthopedic surgical system forsurgical operations.

While the disclosed embodiments are described herein primarilypertaining to tracking orthopedic anatomical structures using theacoustic tracking systems of the present technology to facilitateunderstanding of the underlying concepts, it is understood that thedisclosed embodiments can also include tracking of other anatomical ornon-anatomical structures from which specular information can beobtained, which may include, but are not limited to, pliable regions ofa body, a body wall, or organs (e.g., kidneys, bladder, etc.).

Exemplary Embodiments of the Disclosed Acoustic OTS

FIGS. 1A and 1B show a diagram and an image of an exemplary acousticorthopedic tracking system (OTS) 100, respectively. The acoustic OTS 100includes an acoustic transducer array and supporting structure 110, alsoreferred to as the “structure”, configured to conform to a user's body,including an arm or leg extremity, head, neck, breast, torso or otherbody part, and used by the acoustic OTS 100 for acquiring acousticimaging data, e.g., for producing an acoustic image, range-Dopplermeasurements, and/or feed into a therapeutic systems such as anorthopedic surgical system for affecting surgical operations. Theacoustic OTS 100 includes a signal interface module 120 to provide aninterface between the acoustic transducer array structure 110 and asignal generator and processing device 140 (shown in FIG. 1C). Thesignal interface module 120 can include a signal processing circuitryand components to amplify, multiplex, convert analog-to-digital (A/D)and/or convert digital-to-analog (D/A), or otherwise condition theelectrical signals to be transmitted by and received from the acoustictransducer elements of the array for signal transmission and receptionwith the signal generator and processing device 140.

The signal generator and processing device 140 includes a transmit andreceive electronics unit 142, and a data processing unit 144, as shownin the block diagram of FIG. 1C. Some examples of the transmit andreceive electronics unit 142 (of the generator and processing device140) of the present technology are described in International (PCT)Application Publication No. WO 2016/149427, which is incorporated byreference in this patent document. One example includes a syntheticaperture ultrasound/acoustic (SAU) system 100 shown in FIG. 1 of theabove PCT Publication (reproduced as FIG. 1E in this document), in whichthe SAU system 100 includes a transmit/receive electronics module (TREM)110E in electrical communication with an acoustic probe device 120E andwith a data processing unit resident on the TREM 110E or an externalcomputer device 130E. The TREM 110E is configured to generate theindividual coded waveforms on multiple channels transferred to the probedevice for transmitting and receiving one or more composite waveforms(e.g., coherent, spread-spectrum, instantaneous-wideband, codedwaveforms) based on the individual generated coded waveforms. Inimplementations of the acoustic OTS 100, the probe device can includethe acoustic transducer array structure 110. The TREM 110E includes awaveform generator unit that includes a function generator and anarbitrary waveform generator (AWG). The TREM 110E includes a systemcontrol unit to control the waveform generator unit for the synthesis ofindividual coded waveforms. The TREM includes signal conditioning andprocessing circuitry to amplify, select, and/or convert analog anddigital signals, e.g., which can include analog/digital converters,multiplexers, amplifiers, etc. The TREM 110E includes a data processingunit (e.g., processor or microcontroller, and memory) is configured totransfer data with a central processing unit (CPU) of the computer 130E,e.g., such as executable instructions on waveform synthesis or probecontrol, and/or acquired or processed data.

Referring back to FIG. 1A, the acoustic OTS 100 includes a connector 130(e.g., cable) in communication with the acoustic transducer arraystructure 110 and the signal interface module 120 to provide datacommunications (e.g., transfer the electrical signals) between thestructure 110 and module 120. In some implementations of the connector130, for example, the connector 130 is strain relieved and includesattachable and detachable termini to be coupled to the structure 110with one or more seals to prevent contaminants from intruding. In someembodiments, for example, the outer covering material of the connector130 can be configured of autoclavable material to allow forsterilization. In some embodiments, for example, the connector 130 canbe permanently attached to the structure 110, e.g., which may includethe autoclavable material on the outer covering, or be configured ofmaterials compatible with being disposed (e.g., for one-time use).

FIG. 1C shows a block diagram of an example embodiment of a system ofthe present technology that may be implemented in conjunction with anexternal device or system 150, e.g., such as an orthopedic surgicalsystem for surgical operations. The system includes the acoustic OTS 100and the signal generator and processing device 140. The acoustictransducer array structure 110 is connected (e.g., via the signalinterface module 120) to the transmit and receive electronics unit 142of the signal generator and processing device 140, e.g., through abi-directional analogic and/or digital signal lines. The transmit andreceive electronics unit 142 can include circuitry and electroniccomponents including, but not limited to, power amplifiers, RFamplifiers, variable gain amplifiers, diplexers, multiplexers, digitalto analog converters, analog to digital converters, ASICs, FPGAs, DSPs,RF transformers, analog filters, digital filters, Ethernet circuitry,PCI circuitry, digital buffers, RAM, nonvolatile memory, communicationcomponents, and power supply electronics. The transmit and receiveelectronics unit 142 is in communication with a data processing unit 144of the signal generator and processing device 140 to process and storedata of the device 140.

In some embodiments of the device 140, the data processing unit 144 maybe resident on one or more computers (e.g., desktop computer, laptopcomputer, a network of computer devices in data communication with eachother via the Internet (e.g., in the ‘cloud’), or other computing deviceincluding, but not limited to, a smartphone, tablet, or wearablecomputing/communications device). In some embodiments of the device 140,the data processing unit 144 may be resident in a device structure(e.g., housing) that includes the transmit and receive electronics unit142. The transmit and receive electronics unit 142 is in communicationwith a data processing unit 144 via a digital interface, e.g., which maybe any interface or collection of interfaces including but not limitedto USB, FireWire, Ethernet, PCI, IEEE 1394 Serial, Wi-Fi, Fiber Channel,fiber optics, a wireless bus, a serial bus, or a parallel bus.

The data processing unit 144 may include a programmable processing unitand storage device that may include, but is not limited to, thefollowing components, e.g., one or more processors, serial processors,parallel processors, math co-processors, general purpose graphicalprocessing units (GPUs), FPGAs, ASICSs, DSPs, nonvolatile memory, RAM,digital buffers, storage devices, hard drives, USB, FireWire, Ethernet,PCI, IEEE 1394 Serial, Wi-Fi, Fiber Channel, fiber optics, a wirelessbus, a serial bus, external display adaptor, external display driver, aparallel bus, communications components, and power supply electronics.In some embodiments, for example, the device 140 may also include adisplay device 148, e.g., such as a monitor, speaker, or other device toproduce a combination of visual, audio or haptic output. For example, insome embodiments, the display device 148 may be incorporated togetherwith the data processing unit 144 when the data processing unit 144 isresident on a computer, e.g., such as in a single unit or separatelythrough cabling to an external display.

The data processing unit 144 is configured to process the acquiredacoustic data from the acoustic OTS 100 to produce a data set of theorthopedic structure (e.g., bone) or feature of the subject includingbiological and positional information, e.g., such as bone shape,density, location, orientation, and/or structural movement of featuresand the overall bone. The data processing unit 144 can provide theproduced data set to the external device 150. For example, in someimplementations, the system produces the data set for providing theinformation in real-time to the external device 150 for a diagnostic ortherapeutic application.

FIG. 1D shows a block diagram of an example embodiment of the dataprocessing unit 144. In this example, the data processing unit 144include a processor 182 to process data and a memory 184 incommunication with the processor 182 to store data. For example, theprocessor 182 can include a central processing unit (CPU) or amicrocontroller unit (MCU). For example, the memory 184 can includeprocessor-executable code, which when executed by the processor 182,configures the data processing unit 144 to perform various operations,such as receiving information, commands, and/or data, processinginformation and data, and transmitting or providing information/data toanother entity (e.g., external device 150). To support various functionsof the data processing unit 144, the memory 184 can store otherinformation and data, such as instructions, software, values, images,and other data processed or referenced by the processor 182. Varioustypes of Random Access Memory (RAM) devices, Read Only Memory (ROM)devices, Flash Memory devices, and other suitable storage media can beused to implement storage functions of the memory 184. The memory 184can store data and information of the data processing unit 144 and otherunits of the device 140. For example, the memory 184 can store deviceunit parameters, and hardware constraints, as well as softwareparameters and programs for operation on the device 140. In thisexample, the data processing unit 144 includes an I/O unit 186 that canallow communicative connectability of the data processing unit 144 toother units of the device 140. For example, I/O unit 186 can provide thedata processing unit 144 to be in communications with other devices orsystems, e.g., using various types of wired or wireless interfacescompatible with typical data communication standards, for example,including, but not limited to, Universal Serial Bus (USB), IEEE 1394(FireWire), Bluetooth, IEEE 802.111, Wireless Local Area Network (WLAN),Wireless Personal Area Network (WPAN), Wireless Wide Area Network(WWAN), WiMAX, IEEE 802.16 (Worldwide Interoperability for MicrowaveAccess (WiMAX)), 3G/4G/LTE cellular communication methods, and parallelinterfaces. The I/O unit 186 can also provide communicativeconnectability of the data processing unit 144 to an external interface(e.g., the external device 150), source of data storage, or displaydevice (e.g., the display device 148). The I/O unit 182 of the dataprocessing unit 144 can also interface with other external interfaces,sources of data storage, and/or visual or audio display devices, etc.,to retrieve and transfer data and information that can be processed bythe processor 182, stored in the memory 184, or exhibited on an outputunit of the device 140 (e.g., display device 148).

Referring back to FIG. 1C, in some embodiments, the system includes aposition tracking device 146 to provide data to the data processing unit144 used to determine the location coordinates, orientation, and otherposition and motion information of orthopedic structures of the bodypart with 6DoF. The data processing unit 144 is in communication withthe position tracking device 146, e.g., which can be configured througha digital interface. The position tracking device 146 is operable totrack the position of the acoustic transducer array structure 110 of theacoustic OTS 100, e.g., including the position data of individual arrayelements 111 disposed in the structure 110. In some implementations forexample, the position tracking device 146 can measure the position ofthe acoustic transducer array structure 110 by employing a non-contactsensor of the device 146 to obtain data of the structure 110 and/or bodypart to which the structure 110 is attached. Examples of the sensor ofthe position tracking device 146 can include, but is not limited to, anoptical sensor (e.g., video camera, CCD, LED, etc.), a magnetic sensor(e.g., magnetometer, Hall effect sensor, MEMs-based magnetic fieldsensor, etc.), rate sensor (e.g., gyro sensor, accelerometer, etc.),and/or electromagnetic, radio-frequency, and/or microwave sensors, orother detectors. The position tracking device 146 is configured toprovide the data processing unit 144 with processed coordinateinformation or with the raw sensor data for the data processing unit 144to process to produce the coordinate information of the structure 111and/or body part. The data processing unit 144 is operable to processthe coordinate information with the received acoustic echoes obtainedfrom the acoustic OTS 100 to generate 6DoF coordinate estimates of thebone location, error estimates, acoustic images, and other relevantparameters of the orthopedic feature of the subject, e.g., with anupdate rate of 1 kHz or higher. The data-processed 6DoF bonecoordinates, orientation and/or other information (e.g., relevant to aspecific application) may be communicated by the data processing unit144 of the device 140 to the external device 150 for use by the externaldevice 150.

One example of the position tracking device 146 can include the StrykerSurgical Navigation System (SNS), e.g., such as the Stryker NAV3iPlatform. The Stryker NAV3i Platform includes digital camera technology,positional data processing devices, and multiple visual display monitorsfor tracking in real time. For example, the Stryker NAV3i Platformincludes a navigation camera arm with one or more cameras (e.g.,Built-in LiveCam) for imaging over a large range of motion, e.g., toaccommodate various procedures and approaches. For example, the dataprocessing devices of the Stryker NAV3i Platform include an industrialcomputer (e.g., with high-end processing speed and RAM) and IO Tabletuser interface with touch capability, e.g., with wireless integration(e.g., DICOM query/retrieve and DICOM client functionality for smoothintegration into a hospital network) and various I/O outputs (e.g.,HDMI, etc.) to other data processing devices, e.g., such as the dataprocessing unit 144 of the device 140.

FIG. 2A shows a schematic of an exemplary acoustic transducer arraystructure 110, showing top, side and cross-sectional views of thestructure. The acoustic transducer array structure 110 includes an arrayof transducer elements and a housing body 119 to contain and positionthe transducer elements 111 for transmitting and receiving acousticsignals to/from a mass to which the acoustic transducer array structure110 is applied. The housing body 119 includes a curved section where thetransducer elements 111 of the acoustic transmit and/or receivetransducer array are positioned, where the curved section of the housingbody 119 can be configured to various sizes and/or curvatures tailoredto a particular body region or part where the structure 110 is to beapplied in acoustic imaging, measurement, or other implementations. Forexample, the length, depth, and arc of the curved housing body 119 canbe configured to make complete contact with a region of interest on ananatomical structure, e.g., such as a breast, arm, leg, neck, throat,knee joint, hip joint, ankle, waist, shoulder, or other anatomicalstructure of a human or animal (e.g., canine) subject to image or applyultrasonic treatment to target volumes within such structures, such assplenic masses, cancerous or noncancerous tumors, legions, sprains,tears, bone outlines and other signs of damage or maladies.

FIG. 2B shows a diagram of the acoustic transducer array structure 110coupled to the acoustic coupler 112 to interface with a receiving bodyfor acoustic signal transmission and reception. The acoustic coupler 112is coupled to the transducer elements 111 of the acoustic transducerarray structure 110 creating an acoustic signal transmission interfacebetween the structure 110 and the receiving body (e.g., subject's bodypart). The transducer elements 111 are attached to the housing body 119via a flexible bracket 118. The acoustic coupler 112 is able to conformdirectly onto the face of the transducer element 111, as illustrated inthe diagram. In this example, the acoustic coupler 112 is attached toclip components of the flexible bracket 118 by an adhesive 113 on theexternal surface of the clips, e.g., to align in contact with the ‘tackyregions’ of the hydrogel and/or outer lining of the acoustic coupler112. The clips are configured to attach around the lip of the housingbody 119 to provide direct contact between the acoustic coupler 112 andthe face 111B of the transducer element 111. The transducer element 111can include a transducer acoustic backing portion 111A that interfaceswith electrical communication elements for transduction of electricalto/from acoustic energy.

FIGS. 3A-3D show diagrams illustrating the exemplary acoustic OTS ormultiple acoustic OTSes donned around a patient's leg to determine thetopography of the bone, orientation of the bone in space, or otheranatomical parameters of the patient's leg extremity. FIGS. 3A and 3Bshow various three dimensional views of the acoustic OTS 100 attached tothe femur of a subject, which could be during a diagnostic and/ortherapeutic procedure. FIG. 3C shows 3D view of a portion of thedisclosed system employing two arrays of transducers per leg, includingattaching two acoustic transducer array structures 110 on the leg: onefor tracking the tibia and one for tracking the femur. FIG. 3D shows a3D view of a break-out diagram depicting the example acoustic OTS 100and the acoustic coupler 112 with respect to the subject.

Example features of the disclosed system, including the acoustictransducer array structure 110, the signal generator and processingdevice 140, and/or the position tracking device 146, are furtherdescribed for various embodiments and implementations of the presenttechnology.

The acoustic transducer array structure 110 includes ultrasoundtransducers that are affixed to a frame or housing body 119 (shown inFIG. 2B, for example), and is configured to fully or partially surrounda body part containing one or more bones. The structure 110 can beconfigured to be curved or approximately curved, for example, as in theshape of a circle or ellipsoid. The curved structure may be open, forexample, to cover 120 or 270 degrees around the body part. The openingmay provide utility for accessing specific regions of the body, forexample, for accessing a hip bone. In some embodiments, for example, thestructure 110 is circular and covers 360 degrees around the bone. Thestructure 110 may be flexible, semi-flexible or rigid.

In a flexible embodiment, the structure 110 conforms arbitrarily to thebody part, for example, like a sleeve. Transducers attached to aflexible material enable this embodiment. The flexible materials mayinclude, but are not limited to rubbers such as, latex rubber, nitrilerubber, neoprene rubber, silicone rubber, and combinations thereof.Flexible materials may also include polymers, plastics, and resins.Flexible circuits and flexible coaxial cables enable flexible electricalconnections to the transducers.

In a semi-flexible embodiment, for example, the structure 110 maycontain hinges or pivot points between rigid sections that containtransducers, similar to chain links in a chain. The degrees of freedomprovided by the semi-flexible design allow the structure 110 to conformto a variety of shapes. Position encoders located on each pivot pointenable measurement of relative or absolute angle between adjacentsections. It is noted that 6DoF refers to a Cartesian coordinate systemwith three dimensional spatial coordinates according to 3 orthogonalaxes, e.g., commonly referred to x, y, and z axes, plus a rotation angleabout each respective axis, commonly referred to as roll, pitch, andyaw, respectively.

In a rigid embodiment, for example, the structure 110 may be a fixedshape, such as a circular or elliptical ring or an approximatelycircular or elliptical polygon. The rigid embodiment of the structure110 is structurally inflexible in all dimensions.

In some embodiments, for example, the structure 110 supports ultrasoundtransducers such that the 6DoF position of all transducers are either aknown, measured, or calibrated quantity relative to one or moredesignated points on the support structure. In other embodiments, forexample, the 6DoF location of each transducer is measured dynamicallywith respect to one or more external spatial reference points.

Particularly in the flexible embodiment, but notwithstanding the rigidand semi-rigid embodiments, the distance from an external referencepoint to points on the transducers 111 or the housing body 119 of thestructure 110 can be measured dynamically, for example, using one ormore, but not limited to, optical imaging cameras (e.g., CCD), opticalsensors (e.g., photodiodes), optical patterns (e.g., QR codes), lightemitting diodes, fiber optics, quantum dots, florescent particles,magnetic sensors (e.g., magnetometers, Hall effect sensors, MEMS-basedmagnetic sensors, etc.), magnetic particles, magnets, electromagnets,magnetic nanoparticles, gold nanoparticles, MEMS sensors, capacitivesensors, electromagnetic sensors, microwave sensors, and combinationsthereof. For such measurements, distances are measured to the structurefrom one or more common spatial reference points with known 6DoFcoordinates. The 6DoF coordinates corresponding to each measurementpoint on the structure are triangulated from three or more distancemeasurements. For example, measurement uncertainties for each transduceror structure are approximately reduced in proportion to the square rootof the total number independent measurements made per transducer orstructure, if for example, each transducer has multiple sensors ormeasurement points in order to enable triangulation of the 6DoFcoordinates. Coordinate transformations from one or more spatialreference points to one or more measurement points on the structure toeach individual transducer are computed in real-time and stored fordetermining the position of the bone relative to one or more spatialreference points. The order of the coordinate transformations may followseveral methods or formalisms to reach the same result, e.g., usingdirection cosines, Euler angles, or quaternions.

The shape of the structure 110 may be optimized to accommodate specificbody parts. The structure 110 may embody ergonomic shapes and sizesspecific to various populations, e.g., females or males. In someembodiments, for example, the body part slips through the inner diameterregion of the structure 110 up to the point where the bone will betracked. For example, an acoustic transducer array structure to measurethe tibia slips over the foot, ankle, past the calf muscle to a regionapproximately 3-6 inches below the knee joint. The structure may besized to accommodate specific size ranges of certain body parts, forexample (e.g., calf muscles ranging from 6 to 10 inches in diameter).

The structure 110 may be fabricated from a variety of materials, e.g.,including but not limited to combinations or composites of aluminum,titanium, stainless steel, polymers, fiberglass, plastics, rubbers,glass, or resins.

The structure 110 is designed to move with the body part as the bodypart is moved. For example, when the structure 110 is positioned aroundthe thigh and hamstring region containing a femur bone, and as the legis manipulated, the structure 110 is able to move with the leg such thatangular excursions will not cause a detrimental effect on the acousticdata acquisition. For example, the structure 110 can be configured to beof lightweight in order to minimize mechanical momentum as the body partcontaining the bone is moved.

The structure 110 has freedom of motion with respect to the bonecontained within the body part. The range of motion of the structure 110with respect to the bone may be limited by the method of attachment ofthe structure 110 to the body part. For example, if the structure 110 istaped to the body part, the structure 110 approximately follows the bodypart as it is moved, but the flexibility in the tape and flexibility ofthe skin and underlying soft tissue allows for motion of the structure110, although limited motion. In some embodiments, for example, thestructure 110 is designed to have at least a limited freedom of motionwith respect to the bone (contained within the body part), but thestructure 110 is not rigidly coupled to the motion of the body part orbone contained within the body part. In operations, for example, thetime dependent 6DoF coordinates of the bone can be estimated relative tothe structure 110, and the 6DoF coordinates of the structure 110transform the 6DoF coordinates of the bone to a fixed point in space ateach instant in time. Such operations can be implemented, which are incontrast to obtaining through static or time-independent transformationsapplied to the time dependent 6DoF coordinates of the structure 110.Also, for example, the motion of the structure 110 relative to the bonecan be operated such that such motions are limited, e.g., to prevent thestructure 110 from detaching from of the body part. The structure 110may be attached to a body part in a specific region where the bonecontains features that are more easily tracked compared to anotherregion.

The non-rigid coupling of the structure 110 relative to the bone hasadvantages over other means of rigid coupling. Most importantly, forexample, the coupling is non-invasive. Also, for example, the non-rigidcoupling of the structure 110 does not require methods associated withsurgery, such as incisions, drilling, injections, metal screws, metalrods, temporary implants, permanent implants, and sutures. Non-rigidcoupling of the structure 110 also protects the body from damage, e.g.,such as bruising, infections, bleeding, blood clots, contusions, andscar tissue. The non-rigid coupling of the structure 110 is alsonaturally ergonomic and is configured to automatically find the lowestmechanical stress to both the structure 110 and the body part to whichit is to be attached, where a mechanical system referred to hereincludes the structure 110, the acoustic coupler 112, the body part, thebone, and the component of the structure 110 used to affix the structure110 to the body part and allow limited movement. For example, couplingacoustic energy from the structure 110 into an irregularly-shaped bodypart uses an acoustic coupling material, for example, such as a hydrogelthat is flexible, elastic, and deformable.

In some embodiments, for example, the structure 110 may be cylindrical,with a variable or fixed height so as to accommodate different bodyparts and for affixing the structure 110 containing the transducer tothe body part. The structure 110 may be temporarily affixed to the bodypart. For example, the acoustic transducer array structure 110 caninclude a securement component to affix the structure 110 to the bodypart, in which the securement component can include, but is not limitedto, tape, adhesives, straps, buckles, snaps, buttons, Velcro, and cuffs,and combinations thereof.

Flexible cylindrical extensions from a circular ring structure, e.g.,rubber cuffs, may be used to hold the structure 110 to the body part.The inner diameter of the cuffs may be slightly smaller than thecircumference of the body part so as to slip over the body part and holdit firmly around the entire circumference. The rubber cuff may form aseal around the entire body part so that the void between the patientand the structure containing the transducers may be filled with a liquidor semi-liquid acoustic coupling medium. The cuff may be made from pureor composite elastic materials, including, but not limited to rubberelastomers, silicone, polyurethane, latex, neoprene, natural rubber,fabrics, nylon, silk, or cotton. Said cuff may be autoclavable for reuseor disposable for one use only. Materials compatible with autoclavingand chemical sterilization are well known in the field of medicaldevices.

An acoustic coupling medium is necessary to couple acoustic energythrough the skin and soft tissue between the transducers and the bone.The acoustic coupling medium 112 of the disclosed technology may includeseveral materials, e.g., including, but not limited to water, polymers,organic solvents, organic chemical compounds, inorganic chemicalcompounds, and combinations thereof. The acoustic coupling medium 112may specifically contain water, acrylamide, bisacrylamide, PVA, PVP,DMSO, propylene glycol, sodium benzoate, sodium alginate, sodium borate,sodium chloride, ammonia persulfate, calcium sulfate, magnesium sulfate,tetramethylethylenediamine (TMED), chitosan, acetic acid, ethanol,polyethylene glycol, sorbitol, dextrose, and aloe vera, and combinationsthereof. The acoustic coupling medium 112 may contain organic orinorganic chemical compounds or particles to render it bacteriostatic.

The acoustic coupling medium 112 may be liquid or a gel with a soundspeed and acoustic impedance similar to that of soft tissue. In someembodiments, for example, the sound speed provided by the acousticcoupling medium 112 ranges from 1450 to 1590 m/s to accommodate softtissues, e.g., ranging from fat to muscle, respectively. In someembodiments, for example, the acoustic impedance ranges from 1.3 to 1.7MRayl (kg/(sec·m²)×10⁶) to accommodate soft tissues ranging from fat tomuscle, respectively.

The acoustic coupling medium 112 may include a pre-formed gel material,for example, a cylinder of hydrogel. In some embodiments, for example,the hydrogel may primarily include PVA and water subjected to severalfreeze thaw temperature cycles in order to crosslink the polymer andform a gel.

Prior to temperature cycling, the PVA solution is poured into a mold. Asthe mold is customizable using 3D printing technology, the shape of theexemplary hydrogel acoustic coupling medium 112 may be tailored toindividual body parts and specific transducer structures. For example,the tibia presents a variable thickness of soft tissue around the legwhere the tissue is thin at the shin and thick at the calf. Avariable-thickness cylindrical hydrogel pad may be formed to provide avariable standoff path around the tibia so as to be thick at the shinand thin at the calf in order to place the acoustic focal region at thebone surface. Three-dimensional tomographic imaging information may beutilized to ergonomically tailor a gel pad to each patient.

In some embodiments, for example, the hydrogel adheres to the skin suchthat it may be removed with force, but not enough force to injure theskin or cause discomfort. The hydrogel has sufficient water and ioniccontent to keep the skin hydrated and flexible for long periods of timeso as to minimize discomfort and acoustic artifacts at the gel-skininterface. The hydrogel has a groove or slot that accepts the ultrasoundtransducers and supporting structure with acoustic gel applied to thetransducers. The structure is affixed to the body part by aforementionedtemporary securement component.

Additional information and examples pertaining to the acoustictransducer array and structure device and acoustic signal transmissioncouplant devices of the present technology are described in the U.S.Patent Application Publication No. 2016/0242736, which is incorporatedby reference in this patent document.

In some embodiments, for example, the acoustic transducer arraystructure is an integrated device including ultrasound transducers and arigid supporting structure or frame and is enclosed in a casing portionthat protects the electronics and transducer elements from mechanicaldamage. An acoustically compatible polyurethane or similar material maybe employed as the outermost coating and to seal the enclosure up towhere the cabling enters the device. The thickness, acoustic impedance,attenuation, and sound speed of the polyurethane coating on thetransducers is controlled to optimize sound transmission as part of oneor more acoustic matching layers present on each transducer. Theconnector 120 (e.g., cabling) can be configured to be strain relievedand captured into the device with one or more seals to preventcontaminants from intruding. The entire acoustic transducer array 110 upto the cabling may be autoclaved or chemically sterilized to allow forits reuse on multiple patients. Materials compatible with autoclavingand chemical sterilization are well known in the field of medicaldevices.

The transducers 111 convert electrical energy to acoustic pressure wavesand acoustic pressure waves into electrical energy. Severalpiezoelectric materials may be used in the transducers 111, and areefficient electroacoustic transducers, e.g., including, but not limitedto lead zirconate titanate (PZT), lead zinc niobate and lead titanate(PZN-PT), lead magnesium niobate and lead titanate (PMN-PT), lithiumniobate, barium titanate, and lead metaniobate. The polymerpolyvinylidene fluoride (PVDF) is also known to have goodelectroacoustic transduction properties. Some piezoelectric materialsare formed as ceramics with a prescribed grain size, e.g., containingsmall crystals of the specific materials (e.g., PZT) that are sinteredtogether. Other piezoelectric materials are formed from a single crystalof a piezoelectric material (e.g., PZN-PT, PMN-PT, etc.). To optimizeacoustic properties, the transducers may be formed from one or morecomposites of the aforementioned materials combined with materials knownto absorb or dampen acoustic energy (e.g., polyurethane, epoxy, etc.).Such composites may be formed by dicing and sub-dicing the transducerselements with cuts of various widths, lengths, and depths, which arefilled with one or more attenuating materials, in order to isolateand/or attenuate specific vibrational modes. Transducers may befabricated in multiple layers or stacks in order to increase bandwidthand efficiency.

In some embodiments, for example, each transducer 111 includes acircular element with a resonant frequency ranging from 1 to 10 MHz, anda −6 dB, half-amplitude fractional bandwidth ranging from 10 to 120% ofthe resonant frequency. In this example, the circular elements have afixed focal depth and produce an acoustic beam with radial symmetryabout the central axis perpendicular to the plane of the circularelement. The circular elements have a preferred combination of centerfrequency of transmission, element diameter, and geometric focal depth,such that the range over which the acoustic field is focused, also knownas the depth-of-focus or depth-of-field, includes the tissue-boneinterface. The focal depth, also known as the Fresnel distance, anddepth-of-focus also limit the center frequency and bandwidth due toexpected frequency and depth-dependent attenuation, which may range fromabout 0.2 to over 1 dB/cm/MHz. For example, a bone located in shallowtissue is ideally located using a high center frequency such as 8 MHz,compared to a bone located deeply in tissue, which may be ideallylocated using a 2 MHz center frequency. Preferably, the attenuation atthe maximum expected depth of the bone is not greater than 60 dB so asto accommodate a reasonable receiver gain. The circular elements arepreferably matched to the impedance of the acoustic coupling medium 112with one or more matching layers in order to maximize powertransmission. Furthermore, the circular elements may be geometricallyfocused by either forming them into a concave shape or with the additionof a lens with a sound speed less than or greater than the acousticcoupling medium 112. For the purpose of maximizing the contact of thelens with the acoustic coupling medium, it is preferable to form thelens as a convex lens with sound speed less than the acoustic couplingmedium such that the convex shape will make better contact with theacoustic coupling medium with less possibility of trapping air bubbles.For example, the purpose of lowering the side lobes of the spatialresponse of the circular element to below the standard first side lobelevel of −17.5 dB, it is preferable, but not necessary, to include anapodization property to the acoustic lens or within one or more matchinglayers so as to reduce the side lobe level. The apodization isaccomplished by including a material that has a variable attenuation asfunction of radius across the circular area of the transducer. Variableattenuation is accomplished by incorporating acoustic absorbing materialwith varying amounts as a function of radius. Such materials include,but are not limited to, micron-sized air bubbles, micron-sizedmicroballoons of air, micron-sized particles of, but not limited to,rubber, plastic, glass, metal, and ceramic.

In some embodiments, for example, the number of circular transducerelements arranged on a circular ring structure is at least 16 (e.g., andin some embodiments, 32 or greater), as the standard error indetermining the position of the bone is proportional to the square rootof the number of independent measurements—thus 0.25 times the standarderror for 16 elements and 0.125 times the standard error for 64elements. The number of elements is largely dictated by the elementdiameters, as dictated by several relevant design parameters asdiscussed previously, and the circumference of the inner lumen of thering. Using equations for circular ultrasonic transducer design, tradestudies can be formulated to explore element diameters and centerfrequencies that can be used for a particular set of constraints. Forexample, to achieve a Fresnel distance ranging from 4 to 6 cm, adepth-of-field calculated as 4/3^(rds) the Fresnel distance ranging from5.3 cm to 8 cm, and a two-way attenuation of less than 40 dB, assumingtwo-way attenuation of 1.0 dB/cm/MHz, the approximate element diametersand center frequency combinations that satisfy the aforementioned designconstraints include, but are not limited to, 6 mm diameter at 8 MHz, 6-7mm diameter at 7 MHz, 7 mm diameter at 6 MHz, 5 mm diameter at 5 MHz,8-9 mm diameter at 4 MHz, 10-11 mm diameter at 3 MHz, 12-13 mm diameterat 2 MHz, 16-19 mm diameter at 1 MHz. FIG. 4 shows a diagramillustrating an example of the trade study.

As demonstrated in various example implementations of the presenttechnology, several possibilities exist for element diameter and centerfrequency. The goal of the bone tracking approach is to maximize thepotential for specular reflection from the bone and minimize thepotential for Rayleigh scattering or Rayleigh-like scattering fromwithin the bone itself. As the acoustic transmission coefficient forbone is greater than zero, and may be approximately 0.5, a substantialamount of acoustic energy enters the bone and can be scatteredthroughout the structure. As bone is a living tissue, albeit with muchgreater sound speed and acoustic impedance compared to soft tissue,scattering from within the bone is similar to Rayleigh scattering insoft tissue; however, bone has much greater frequency anddepth-dependent attenuation ranging from 4-8 dB/cm/MHz. Thus, highercenter frequencies are preferred to minimize the potential for Rayleighscattering from within the bone.

Contrastingly, the potential for specular scattering is maximized forlarger beam diameters, which cover a larger area over the bone surface,which increases the possibility of finding a flat or approximately flatregion from which a specular reflection is received. The −6 dB beamdiameter is approximately given by the f-number of the aperture timesthe wavelength, where f-number is approximately given by the Rayleighdistance or focal depth divided by the element diameter. For a constantfocal depth of 5 cm, the aforementioned transducer diameter and centerfrequency combinations have beam widths ranging from approximately 4-4.7mm for the 1 MHz designs to approximately 1.6 mm for the 8 MHz design.

For example, a trade exists for center frequency and element diameterversus specular scattering potential versus Rayleigh scatteringpotential. A preferable design based on aforementioned constraints wouldfall somewhere between the extremes, for example, a 5 mm diameterelement at 5 MHz with a beam diameter of approximately 1.9 mm. In somecases, for example, it may be preferable to lean higher or lower infrequency. For example, in some cases, it may be preferable to havebeams that approximately overlap at the surface of the bone, thuspossibly requiring a lower frequency or smaller element to widen thebeam.

The transducer elements 111 and configuration of the elements 111 arenot limited to a single ring element placement within a single plane.For example, the elements may be placed along two or more rings suchthat the elements occupy two or more planes in a cylindricalarrangement, e.g., so as to track bone echoes along two or more planesalong the length of a femur. The individual rings of elements occupyingeach plane may also be staggered with respect to the neighboring ring soas to distribute spatial samples more uniformly around the bone, forexample, in a helical pattern or helical-like pattern such as a spiral.Likewise, the elements may be placed to achieve a periodic spatialsampling such that the angle between the elements is constant, forexample, with 11.25 degrees separating 32 elements to span a full 360degrees around the bone. Such a constant sampling arrangement would beapplicable to tracking a femur bone, which is roughly circular.Applications where the optimal spatial sampling of the transducers isaperiodic or non-uniform or spatially diverse in three dimensions may beenvisioned for tracking specific bones such as the hip bone, which doesnot conform to a circular geometry.

In some embodiments, for example, the transducer elements 111 arearranged in the same plane with each other such that all are pointing atthe same point in space. In other embodiments, for example, thetransducer elements 111 are fixed to point at angles determined tomaximize specular reflections in the acoustic echoes from a particularbone. For example, the cross-section of the tibia is not round, butrather, approximately triangular. Transducer elements may be arranged topoint along 3D vectors required to maximize the specular reflection fromthe surface of the tibia.

In some embodiments, for example, the location of the bone is maintainedwithin the depth-of-focus with use of an acoustic coupling medium, e.g.,a hydrogel. The elastic hydrogel coupling medium 112 may conform toirregularities in the body part and soft tissue surrounding the bone.The example hydrogel coupling medium 112 may be ergonomically designedand molded to fit a particular application.

Different transducer array configurations and geometries may beenvisioned. Arrays may include hundreds or thousands of elementsarranged in a circular or ellipsoidal or curved aperture that is eitheropen or closed. For example, instead of using a single element to focusan acoustic beam, focusing may be achieved using suitably delayedtransmissions from several small transducers elements arranged in one ormore 1D, 1.25D, 1.5D, 1.75D, 2D, or 3D linear or phased arrays, asconsistent with the current state-of-the-art in clinical ultrasoundscanners. Linear arrays typically have a pitch or spacing betweenelement centers of one wavelength or more, and phased arrays have apitch of less than one wavelength, and preferably one-half wavelength orless to allow for steering the acoustic beam. The operating of linear orphased arrays can be either in full or partially synthetic aperture modeas commonly implemented in clinical ultrasound scanners. The disclosedsystem is not limited to a specific means or aperture dimension fortransmitting or receiving acoustic energy. Moreover, the disclosedsystem is not limited to a particular diameter, shape, or size for thetransducer array. The disclosed system is directly applicable topartially or fully beamformed ultrasound images from one or more aspectsor views or angles or directions, tomographic ultrasound over anglesranging from 0 to 360 degrees, synthetic aperture ultrasound, and threedimensional ultrasounds data sets.

Specific embodiments utilizing an array or plurality of arrays oftransducer elements apply specifically to high resolution and high speedorthopedic tracking with circumferential or tomographic coverage of abone, e.g., a femur.

In one embodiment, a 1D array of transducer elements with pitch rangingfrom ½ wavelength to several wavelengths are arranged in a full circleto form a tomographic array. FIG. 5A shows a top view example of such atomographic array. In this arrangement, depending on the electricalconnectivity of the array with regards to both transmission andreception and the number of channels in each case, there are manypossibilities for transmission and reception. Likewise, the targetapplication of the array dictates the required spatial sampling aroundthe circumference of the array. For example, in some cases it may bebeneficial to utilize large elements with a narrow directivity so as tofocus acoustic energy both on transmission and reception along specificdirections or radial vectors defined by the vectors pointing from thecenter of the element to the geometric center of the circular array. Inother cases, for example, it may be beneficial to utilize small elementswith a wide directivity such that the array may operate with, forexample, dynamic focusing and apodization on both transmission andreception.

Generally, the pitch or spacing of the elements must be limited in orderto reduce or eliminate the potential for grating lobes on eithertransmission or reception in either real beam or synthetic apertureoperation when steering is required in beam formation. Consideringorthopedic tracking applications where steering is enabled, an examplearray can contain 1024 transducer elements arranged side-by-side withazimuthal pitch ranging from ½ wavelength to 2 wavelengths that comprisea tomographic aperture with radius equal to approximately 1024 times theelement pitch divided by 2π. FIG. 5B shows a top view examples of suchan array, while FIGS. 5C and 5D show a side view and an isometric viewof such an array. Accordingly, element widths range from ½ wavelength to2 wavelengths minus the space between elements, i.e., the kerf. Elementheights in the elevation dimension may span several wavelengths in orderto provide both passive and geometric focusing ability in elevation,depending on the typical depth and depth-of-focus requirement for aparticular application. The described tomographic aperture is providedfor the purpose of illustrating specific transmission and receptionpatterns. The transmission and reception patterns are equally applicableto arrays that contain arbitrary element sizes and numbers of elementsarranged in a tomographic configuration.

In some embodiments, transmission is enabled on one or more transducerelements, preferably, in the case of more than one element, a contiguousgroup of elements, with electronic delays assigned to each to form asingle focused acoustic beam, i.e., a real beam. FIG. 5E illustrates anexample of such a configuration in which transmission is enabled on acontiguous group of elements. The case of transmission on one element ishandled separately as further described below. The process of beamformation is well known in the art of ultrasound imaging, radar imaging,and signal processing.

In one example, the real transmit beam may result from transmission on64 contiguous elements, e.g., elements 1 through 64, where the focalpoint of the beam falls somewhere within the sector subtended by the arclength and angle spanned by elements 1 through 64, as depicted in theexemplary diagram of FIG. 5F. In this example, transmission on elements1 through 64 can be followed by transmission on elements 2 through 65,as shown in the exemplary diagram of FIG. 5G.

In some embodiments, the transmit beam may step arbitrary increments inelement index, for example, transmission on elements 1 through 64followed by transmission on elements 257 through 320.

In some embodiments, the real transmit beam may be steered arbitrarilyin space by applying suitable delays to each participating transmitelement.

In some embodiments, the real transmit beam may be arbitrarily firedfrom any contiguous group of elements with the virtual center of thetransmit aperture, i.e., phase center, changing from one transmission tothe next with spacing that changes in ways that include, but are notlimited to, stationarily (e.g., 1 1 1 . . . ), incrementally (e.g., 1 23 . . . ), sequentially (e.g., 1 3 5 . . . ), periodically (e.g., 1 5131 513 . . . ), randomly (e.g., 254 46 884 373 109 209 . . . ),repeatedly (e.g., 1 1 1 . . . ), cyclically (e.g., 1 2 3 1 2 3 . . . ),or deterministically (e.g., mod(transmit index, 128)=0).

In one embodiment, the real transmit beam is fired according to asequence that repeats periodically with a defined cycle time.

Following transmission of the real beam, a plurality of elementscomprising the receive aperture is enabled to receive acoustic echoes.In some embodiments, the receive aperture includes one or more elementscentered or approximately centered with the transmit aperture, asdepicted in FIG. 5H.

In some embodiments, the receive aperture follows the transmit apertureas it changes location between transmissions.

Parameters affecting the real beam, e.g., aperture size, apodization anddelays, may be pre-determined according to a priori information, e.g.,an MRI or CT image that gives measurements of distance from the expectedlocation of the transducer elements to the surface of the bone. The apriori information may be used in determining the location of the beamrelative to features on the bone, e.g., normal to a flat region ornormal to the local apex of a curved region.

Additionally, an optimization process can determine the number ofelements involved in a transmission, the transmission delays for eachelement, the transmission amplitudes for each element (e.g., anormalized per-element transmit apodization ranging from 0 to 1). Inparticular, the real beam may be manually or automatically tuned toplace the focal point at the surface of a bone according to focusingmetrics derived from coherently beamforming echoes received from thevicinity of the bone, e.g., echo intensity, echo power and imagecontrast in the vicinity of the bone. Likewise, transducer elementsutilized for reception may also be optimized to determine the optimalnumber of elements involved in reception, the received delays for eachelement, and the weightings of each received echo (e.g., a normalizedper-element receive apodization ranging from 0 to 1).

In some embodiments, the f-number, e.g., the focal depth divided by theaperture size of the transmit and receive aperture is held approximatelyconstant for each beam relative to the focal point aligned with thesurface of the bone for a plurality of points insonified on the bone.For example, to maintain an f-number of 1 for two bone interfaces at 1cm depth and 3 cm depth from points on the array, the aperture sizesmust be approximately 1 cm and 3 cm, respectively. This can be seen withfrom the example diagram in FIG. 5I, where f-number of 1 is maintainedfor two focal points that are at 1 cm and 3 cm, respectively, from thetransmit/receive apertures on two sides of the array. Here aperture sizeis defined by the linear distance measured to points on the most distantelements comprising the aperture, e.g., the chord length.

As an alternative to beamforming with real beams, synthetic aperturebeamforming may be employed. In synthetic aperture embodiments, manypossibilities exist for beam formation. For example, a synthetictransmit aperture may utilized with a non-synthetic receive aperture.Alternatively, a non-synthetic transmit aperture may be used with asynthetic receive aperture. In yet another alternative, a synthetictransmit aperture may be used with a synthetic receive aperture. In someapplications, it may not be feasible to utilize a fully synthetictransmit and receive aperture due to the high number of transmit andreceive combinations that need to be acquired independently.

The high degree of redundant echo information contained within fullsynthetic aperture beamformer samples combined with the limiteddirectivity of transducer elements enables specific embodiments, some ofwhich are further described below.

In one embodiment, transmission from the previously described examplearray is enabled on one transducer element at a time, e.g., in asynthetic transmit aperture format, followed by reception on one or moreelements simultaneously that include the transmit element and elementsto either side of the transmit element. This embodiment differs from theabove described embodiment in that one transmit element is utilizedinstead of a group of transmit elements.

For example, transmission on element 1 is followed by reception on acontiguous group of 64 elements ranging from 993 to 32. Next,transmission on element 2 is followed by reception on 64 elementsranging from 994 to 33. Next, transmission on element 3 is followed byreception on 64 elements ranging from 995 to 34. This pattern iscontinued sequentially until all elements are used for transmission onetime to complete a single cycle.

Without loss of generality, this embodiment also applies to smaller orlarger receive apertures (e.g., 32 or 128 elements), where the transmitelement is approximately centered within the receive aperture, and thereceive aperture steps with the transmit element.

In another embodiment, a special case of synthetic aperture isimplemented for transmission on one element and reception on the sameelement. This embodiment differs from the above described embodiment inthat one transmit element is utilized instead of a group of transmitelements.

Referring to the previously described example array, for example, with acycle starting with transmission on element 1 is followed by receptionon element 1. Next, transmission on element 2 is followed by receptionon element 2. Likewise, transmission on element 3 is followed byreception on element 3. The pattern ends with transmission on element1024 and reception on element 1024 to complete one cycle, after which itis repeated.

In this embodiment, transmission and reception may proceed out ofsequential order, for example, in sequential quadrants. Referring to thepreviously described example array, the cycle may start withtransmission on element 1 followed by reception on element 1. Next,transmission on element 257 is followed by reception on element 257.Next, transmission on element 513 is followed by reception on elements513. Next, transmission on element 769 is followed by reception onelement 769. Next, transmission on element 2 is followed by reception onelements 2. Next, transmission on element 258 is followed by receptionon elements 258. Next, transmission on element 514 is followed byreception on elements 514. Next, transmission on element 770 is followedby reception on elements 770. The pattern continues by increasing theelement index for transmission and reception by one. The pattern endswith transmission on element 1024 followed by reception on element 1024.Each iteration is incremented by one element until all elements are usedfor transmission once to complete one cycle before it is repeated.

Similarly, transmission and reception may proceed out of sequentialorder in other divided manners, including, but not limited tosequentially in haves, quadrants and octants.

Alternatively, transmission may proceed according to a random orpseudorandom permutation of the elements, e.g., 328; 82; 119; 829; 130;91; 848; 485; 4; 238 and so forth until all elements are used fortransmission one time to complete a transmission cycle. For eachtransmission, reception occurs on the transmit element. For example,after transmission on element 328, a reception occurs on element 328.

An important feature of this embodiment is that only 1 transmit channeland 1 receiver channel is required per transmission event, thusdramatically reducing the hardware complexity and volume of data forthis operating mode compared to full synthetic aperture modes thatutilize many more elements on reception. A reduced data rate in turnreduces the time required to transfer echo samples and the time requiredto process the samples, and ultimately, reduces the time lag between thetrue physical location of a target, e.g., a bone, and the estimatedlocation of the target. A high rate of position feedback with low lag isof critical importance in assisted surgery in order to preventcontroller feedback errors due to inaccuracies, undersampling, andhysteresis.

In one embodiment, a second special case of synthetic aperture isimplemented for transmission on one element and reception on twoelements, specifically, reception on the transmit element and on oneimmediately adjacent element. For example, an array containing 1024transducer elements arranged side-by-side with pitch ranging from ½wavelength to 1 wavelength that comprise a tomographic aperture. In thisconfiguration, transmission on element 1 is followed by reception onelements 1 and 2. Next, transmission on element 2 is followed byreception on elements 2 and 3. Likewise, transmission on element 3 isfollowed by reception on elements 3 and 4. The pattern ends withtransmission on element 1024 and reception on elements 1024 and 1 tocomplete one cycle, after which it is repeated. Alternatively, the cyclemay start with transmission one element 1 followed by reception onelements 1024 and 1. Next, transmission on element 2 followed byreception on elements 1 and 2, and so forth until ending withtransmission on element 1024 and reception on elements 1023 and 1024.Reception on both elements preceding and following the transmissionelement is also possible and disclosed herein; however, the acousticecho information is largely redundant for both cases.

In this embodiment, transmission and reception may proceed out ofsequential order, for example, in sequential quadrants with transmissionon element 1 followed by reception on elements 1 and 2. Next,transmission on element 257 is followed by reception on elements 257 and258. Next, transmission on element 513 is followed by reception onelements 513 and 514. Next, transmission on element 769 is followed byreception on elements 769 and 770. Next, transmission on element 2 isfollowed by reception on elements 2 and 3. Next, transmission on element258 is followed by reception on elements 258 and 259. Next, transmissionon element 514 is followed by reception on elements 514 and 515. Next,transmission on element 770 is followed by reception on elements 770 and771. Each iteration in incremented by one element until all elements areused for transmission once to complete one cycle before it is repeated.

Similarly, transmission and reception may proceed out of sequentialorder in other divided manners, including, but not limited sequentiallyin haves, quadrants and octants.

Alternatively, transmission may proceed according to a random orpseudorandom permutation of the elements, e.g., 72; 987; 63; 231; 546;771; 9; 1021; 393; 20 and so forth until all elements are used fortransmission one time to complete a transmission cycle. For eachtransmission, reception occurs on the transmit element, and on thepreceding element or on the following element, e.g., for transmission onelement 72, a reception occurs on elements 71 and 72 or on elements 72and 73. Simultaneous reception on elements 71, 72 and 73 is alsopossible; however, the information contained in echoes recorded forelements 71 and 73 are largely redundant.

An important feature of this embodiment is that only 1 transmit channeland 2 receiver channels are required per transmission event, thusdramatically reducing the hardware complexity and volume of datarequired for this operating mode compared to full synthetic aperturemodes that utilize many more elements on reception. A reduced data ratein turn reduces the time required to transfer echo samples and the timerequired to process the samples, and ultimately, reduces the time lagbetween the true physical location of a target, e.g., a bone, and theestimated location of the target. A high rate of position feedback withlow lag is of critical importance in assisted surgery in order toprevent controller feedback errors due to inaccuracies, undersampling,and hysteresis.

In all real beam and synthetic aperture embodiments, it is onlynecessary to beamform echoes over a narrow range window that includes abone interface. In this regard, multiple transmissions may be staggeredin time in such a way that they are in flight at the same time, thoughspaced apart adequately to prevent overlapping echo samples in thebeamformer, as illustrated in the example configuration of FIG. 5J. Forexample, a range window of 3 cm, is first insonified by a transmissionon aperture 1 followed by a coherent transmission on aperture 2 after aprescribed delay, e.g., 20 microseconds or 3.08 cm in space at soundspeed equal 1540 m/s, followed by reception on aperture 1, followed byreception on aperture 2. FIG. 5K illustrates an example sequence oftransmit and receive signals as a function of time. A high speedmultiplexer may be used to switch reception from apertures 1 and 2.Using this technique, the resulting cycle time required to cover allelements on transmission is divided by approximately a factor of 2.Likewise, additional reductions in cycle time are allowed for eachadditional staggered transmission. For example, 3 staggeredtransmissions reduces the cycle time by approximately a factor of 3. Asan alternative to multiplexing, additional receive channels may beutilized.

The transmission delays utilized to stagger transmissions may be variedrandomly in order to temporally decorrelate coherent echoes fromprevious transmissions, thus producing what is sometimes referred to astemporal dithering in fields such as ultrawideband communications.

In another embodiment, simultaneous transmissions are enabled usingcoded waveforms, specifically, waveforms that are orthogonal, e.g.,their mutual cross correlations are zero or approximately zero for alldelays.

In another embodiment, simultaneous transmissions are enabled usingcoded waveforms, specifically, waveforms that are partially orthogonal,e.g., their mutual cross correlations are zero or approximately zero fora range of delays.

In another embodiment, one or more receptions occur on array elementsthat are between 90 degrees and −90 degrees away from the phase centerof the transmitting aperture, e.g., in a pitch-catch transmit-receivefashion, for the purpose of measuring the time of flight and attenuationfor a given propagation path. As illustrated in FIG. 5L, using the abovedescribed example array, for a transmission on element 1, there are oneor more receptions on elements 257 through 769. A complete cycle of suchtransmissions and receptions comprises a transmission tomographicdataset from which sound speed and attenuation may be estimated and usedfor refining beamformer delays on both transmission and reception.

The disclosed technology includes methods for processing the data, e.g.,using the data processing unit 144 (shown in FIG. 1C), to produce a dataset identifying shape, location, and movement information of anorthopedic structure of a body part from which the acoustic signal datais acquired. Example features of the disclosed method are furtherdescribed for various embodiments and implementations of the presenttechnology.

The example methods for orthopedic tracking are described in generalterms and are applicable to any possible array configuration of theacoustic OTS 100. Acoustic (e.g., ultrasound) pulses are transmittedfrom the plurality of acoustic transducer elements 111 of the structure110, e.g., including sequentially one-at-a-time, simultaneously, or in atime-staggered or time-delayed pattern. Each transmission is accompaniedby receptions of acoustic echoes on one or more of the transducerelements 111 corresponding to a single transmission. In the case of acircular fixed-focus piston transducer, for example, the echoes arereceived only on the same transducer. In the case of a linear or phasedarray, for example, reception occurs on one or more transducerssimultaneously. The received echoes are amplified, filtered, andtemporally sampled sufficiently, e.g., by the device 140, to retain allrelevant spectral information corresponding to the echoes from softtissue and bone as is dictated by the Nyquist sampling theorem. Receivedechoes are digitally sampled and stored for processing.

Preferably, the transmitted pulse contains the widest bandwidthpossible, e.g., around 100% fractional bandwidth, which approximatelycorresponds to an impulse response of a single acoustic cycle. Thereason for the high bandwidth being that the location of specular echoesfrom the bone will have a range uncertainly that is approximatelyinversely proportional to wavelength divided by fractional bandwidth.For example, an 80% fractional bandwidth system operating at 5 MHz has awavelength of 0.308 mm. The range measurement uncertainty for thisexample pulse is approximately 0.308 mm divided by 0.8, which equals0.385 mm. Other sources of measurement uncertainty may include, but arenot limited to, spatial averaging caused by the finite beam size,electronic noise, temporal sampling, quantization noise, side lobes,grating lobes, attenuation, sound speed, and motion. Except in the caseof very high velocities of motion of the array or patient, greater than1 m/s, the bandwidth, wavelength, and sound speed are typically thelargest sources of measurement uncertainty. Using transmitted waveformswith a large time-bandwidth (e.g., spread-spectrum waveforms) productenable deeper penetration at a higher transmitted frequency in order tocompensate for loss in signal-to-noise ratio (SNR) due to frequency anddepth-dependent attenuation.

In some embodiments, for example, the waveforms used belong to a classof waveforms known as spread-spectrum waveforms. Such waveforms arerobust to deleterious factors including, but not limited to, frequencyand depth-dependent attenuation, electronic noise, cross-talk betweenadjacent channels, and acoustic reverberation. For example, waveformscan be transmitted with a pulse-repetition-frequency (PRF) rangingarbitrarily up to about 100 kHz, with the upper end dictated by thesound speed, attenuation, the maximum depth from which the echoescontain useful information, degree of spatial and temporal overlapbetween neighboring transmitted beams (e.g., staggered transmissions),speed of transmit and receive multiplexer circuitry, electroniccrosstalk, and potential tissue heating. The PRF and the number oftransmissions per cycle to adequately insonify independent locations onthe bone dictate the rate at which the OTS provides position feedback onthe 6DoF coordinates of the bone.

Due to the specular nature of bone reflections, echoes from thetissue-bone interface will present a different and identifiable echosignature compared to echoes from soft tissue and from within the boneitself. The specular echo signature from a human femur bone suspended inwater is shown in FIG. 6A, in which these example results were measuredand processed in example implementations of the disclosed system. Here,for example, echoes were recorded using a Philips L7-4 linear arrayoperating at 5 MHz and approximately 80% FBW. The transmission occurredon a single element and echoes were received on the same element. Exceptfor lensing in elevation, there was no focusing in azimuth. Echoes wererecorded every 0.5 degree around the circumference of the bone. Here, aset of transmit angles were isolated over depth to zoom in on theechoes. It was observed that the specular component is approximatelyconstant and remains highly correlated as a function of angle, whereasthe Rayleigh component varies rapidly and decorrelates as a function ofangle. It was also observed that the specular component forms a patternas a function of angle. These observations were a key aspect of thedisclosed technology. Patterns either match the specular component ofthe ultrasound echoes or they do not, for example, as depicted in FIG.6B.

All bones, for example, the femur and tibia, have unique cross-sectionalpatterns over the length of the bone. FIGS. 7A and 7B show exampleradial patterns for a human femur, and FIG. 7C shows an example radialpattern for a human tibia, e.g., as obtained from CT volumes of bothbones. Here, the radii measured to the centroid of the cross-sectionalslice through bone along its length was quantified for 64 anglesspanning 360 degrees. Additionally, the corresponding circumference(denoted perimeter in the original figures internally) of the bones as afunction of length were quantified, as shown in FIG. 7D for the femurand FIG. 7E for the tibia. It was observed that some regions have morerapidly changing circumference than others, particularly close to theknee joint. It is in these regions that the cross-sectional patterns arethe most sensitive and feature rich for bone tracking.

The pattern may be matched to a library of patterns determined from anymeans of tomographically imaging the bone, for example, as determinedfrom a high resolution computed tomography (CT) image of the bone. Thedisclosed method includes a process for matching the specular acousticecho pattern from bone sampled at one or more points on the bone to alibrary of patterns sampled according to the array geometry, e.g., inwhich the process can employ matching the pattern in order to match thetopography of the bone, and thus, estimate the orientation of the bonein 6DoF coordinate space according to the location of the transducersrelative to a fixed point in space. It is important to note that themethod is not “speckle tracking”, as ultrasound speckle is due to randomscattering, which is tracked using correlation between ultrasoundimages. “Specular” and “speckle” refer to different echo properties.

Signal processing is applied to the amplitude and phase informationpresent in the received radio-frequency (RF) echoes to determine apattern match against patterns automatically generated from a threedimensional library containing rigid bone information. Pattern matchingcan be achieved by statistically correlating information in the echosamples to patterns generated from the library. Penalty terms can beplaced on each pattern sample to make the pattern matching robust tovariable sound speed. Information about tissue types between thetransducer and the bone surface can be used to inform the patternmatching algorithm for a more precise match, for example, sound speedinformation obtained from ultrasound tomography or inferred from MRIrelaxation time information or CT Hounsfield unit information. Examplealgorithms may include, but are not limited to, linear crosscorrelation, circular cross correlation, sum-absolute-difference (SAD),linear regression, non-linear regression, first order statistics, secondorder statistics, higher-order statistics, Fourier transform, Mellintransform, Fourier-Mellin transform, Radon transform, Hankel transform,Eigenvalue decomposition, radial symmetry transform, singular valuedecomposition, pseudoinverse (e.g., generalized inverse, Moore-Penroseinverse, etc.), matrix inverse, pivot transformations, orthogonaltransformations, wavelets, wavelet transform, matched filters, Hilberttransform, FIR filters, IIR filters, nonlinear filters, interpolators,and combinations thereof. The algorithms may operate on the amplitude,phase, or both amplitude and phase information contained within theechoes.

The inputs to the algorithm include, but are not limited to, a libraryof three dimensional information about the bone being tracked that issearchable through geometric projections (e.g., ray tracing), 6DoFcoordinate information about the transducer locations, a prioriinformation about the sound speed of the coupling medium and expectedsound speed through soft tissue, timing information about the acousticechoes, amplitude scaling information about the acoustic echoes, andtransmitted waveform information corresponding to each acoustic echo.

The outputs from the algorithm include, but are not limited to, theestimated 6DoF coordinates of the bone being tracker, one or moreconfidence indicators of the pattern match, one or more estimates of theuncertainty in the estimated 6DoF coordinates, and estimates of thetissue and bone velocity and acceleration along the axis of eachtransducer.

In some embodiments, for example, the algorithm may also contain aKalman filter that models the physics of the array and bone movements.Inputs and outputs required of the Kalman filter will also be included,in addition to the aforementioned parameters.

In some embodiments, for example, the algorithm may also contain anoptimizer that efficiently searches through potentially millions ofpatterns using a gradient decent or similar optimization approach.

In one example approach for bone tracking, the algorithm can includeprocesses seeking to optimize several parameters simultaneously. FIG. 8Ais an illustration depicting a simple arrangement of two transducers800A and 800B transmitting and receiving echoes though soft tissue thatcontains a bone. For illustration purposes, the transducers 800A and800B are arranged at 180 degrees with respect to each other; however,the concept is easily extended to multiple pairs of transducers atarbitrary multiple angles. The distance between the centers of theradiating apertures of the transducers given by d₁, which is the onlyknown quantity. The distance from the left transducer to the bone isgiven by d₃=c₃τ₃ and the distance from the right transducer to adifferent point on the bone is given by d₄=c₄τ₄, where c₃ and c₄ are therespective average sound speeds and τ₃ and τ₄ are the respective echotimes to the bone as estimated by the echo pattern match to the 3D bonemodel. The distance d₂ is the measured thickness of the bone asdetermined by the echo pattern match to the 3D bone model. The equationd₁=d₂+d₃+d₄ constitutes a conservation of distance such that the unknownsound speed parameters c₃ and c₄ are estimated. Additionally, as d₂ isdetermined from a rigid model and d₁ is rigidly known, d₁-d₂ istherefore a rigid distance, and d₃+d₄, though not rigidly known, aretaken together as a rigid quantity. Thus, deviations in the estimatedsum of d₃+d₄ from the rigid quantity d₁−d₂ may be assigned a penalty inan optimization cost function such that increasing deviations areassigned a linearly or nonlinearly increasing penalty. As d₃+d₄ are alsofunctions of c₃ and c₄, respectively, linear or nonlinear penaltiesmaybe assessed on c₃ and c₄ and included in the overall cost function.For example, if the average sound speed is known to be 1542 m/s, and thecurrent echo pattern match calls for a sound speed of 1538 m/s, apenalty is assessed on the difference of 4 m/s as a linear or nonlinearfunction of the difference. It is also learned that a change in d₃causes an equal and opposite change in d₄ due to the conservation ofdistance. This assumption is especially true over very short time scalesof 1 millisecond or less, where the movement of the bone is likelybounded to be within 1 mm. Thus, the disclosed method, where the arraysurrounds the bone by at least 180 degrees, is especially robust toindependent movement of the array with respect to the bone. Thedisclosed algorithm, for example, may be extended to an arbitrary numberof pairs of transducers or acoustic beams, with each transducer or beamor collection of transducers of collections of beams having its ownobjective function as shown in FIG. 8B. Here, the goal is to minimizef_(n) over N pairs. It is also seen that f_(n) is a function of the 6DoFcoordinate of the bone as estimated from the pattern matching algorithm.The robustness increases as the number of transducers or beamsincreases. The method is not strictly limited to pairs of transducers orbeams; however, the preferred embodiment consists of a collection ofopposite pairs where the angle between each pair is 180 degrees.

In some embodiments, for example, the disclosed algorithm is as follows.Recorded echoes are processed and one or more pattern matchingalgorithms roughly matches the specular echo patterns to a 3D model ofthe bone of interest to initialize a set of objective functions. Duringthis initial match, the sound speed of the tissue is assumed to be somevalue, for example, 1540 m/s. With the objective functions initialized,a multivariate optimizer determines the best fit to the 3D model byvarying all parameters except for the known distance between each pairof transducer elements. At each iteration, the optimizer refines thesearch of the 3D model over a constrained set of 6DoF coordinatesaccording in order to minimize the set of objective functions that mayinclude one or more penalty terms (not shown in FIG. 7B, but asdescribed above), e.g., a penalty on the sound speed. The optimizer mayalso incorporate additional inputs such as velocity and accelerationmeasured from the acoustic echoes near the estimated location of thetissue-bone interface. The optimizer may also incorporate inputs fromthe real-time estimated velocity and acceleration of the acousticstructure as tracked externally. The optimizer may also incorporateoutputs from a Kalman filter that filters multiple velocity andacceleration inputs to produce a filtered respective velocities andaccelerations. At each iteration, the algorithm outputs parametersincluding, but not limited to, estimated 6DoF coordinates of the bone,pattern match metrics, objective function values, penalty estimates, andestimated velocities and accelerations.

One example applications of the present technology is to track the tibiaand femur bones in the leg during computer assisted surgery (CAS) of theknee, including, but not limited to, total knee arthroplasty (TKA) andtotal knee replacement (TKR). Current state-of-the-art TKA and TKRrequire surgical placement of an alignment rod into both the tibia andfemur for rigidly tracking both bones using external optical trackers.To place the alignment rod, a small incision is made in the skin, a holeis drilled into the bone, and the rod is screwed into the hole. Theprocedure is invasive, resulting in unsightly scarring on the skin. Itpotentially compromises the integrity of the bone, particularly forelderly patients. It is a site of potential infection, which can lead topost-surgical complications. The disclosed system is envisioned toreplace this invasive tracking with non-invasive tracking as describedherein. FIG. 3C shows an example embodiment employing two arrays oftransducers per leg, including attaching two acoustic transducer arraystructures 110 on the leg: one for tracking the tibia and one fortracking the femur.

According to the Anthropometric Reference Data for Children and Adults:United States, 2003-2006, National Health Statistics Reports, No. 10,Oct. 22, 2008, pp. 1-45, the maximum calf circumference is roughly 48 cmor 15 cm in diameter across all ages and races, and the maximummid-thigh circumference is roughly 70 cm or 22 cm in diameter across allages and races. Thus, a fixed, 15 cm diameter array accommodates the legjust above the knee for most of the population, and is large enough toslide over the calf and knee of the majority of the population. Such anarray would operate preferably with a center frequency in the vicinityof 5 MHz.

In some embodiments, for example, the acoustic echoes are displayed onmonitor similar to ultrasound echoes are displayed on a clinicalultrasound scanner. The echoes may be displayed in raw format as RFechoes or in grayscale as log compressed amplitude or B-mode images. Thepattern match may be overlaid on the echoes so the user can observepositioning and pattern matching. A three dimensional rendering of thebone being tracked can also be displayed in real-time as the usermanipulates the body part.

In some embodiments, for example, coordination of acoustic transmission,reception, echo processing, and output communication takes place on anon-transitory computer readable medium that includes a processor, adisplay, a means of digital communication, and electronics for acoustictransmission, electronics for reception of acoustic echoes, andelectronics for recording and storing acoustic echoes.

Additional information pertaining to the disclosed technology isdescribed in a later section of this document under the heading “ASpecific Example An OTS System.”

Examples

The following examples are illustrative of several embodiments of thepresent technology. Other exemplary embodiments of the presenttechnology may be presented prior to the following listed examples, orafter the following listed examples.

In one example of the present technology (example 1), an acousticorthopedic tracking system includes an acoustic probe device structuredto include a support frame having a curved shape to interface a bodypart of a biological subject, and an array of transducer elementsarranged on the curved support frame and operable to transmit acousticwaveforms toward a target volume of an orthopedic structure in the bodypart and to receive returned acoustic waveforms that return from atleast part of the target volume of the orthopedic structure; an acousticcoupling component coupled to the array of transducer elements andoperable to conduct the acoustic waveforms between the transducerelements and the body part of the biological subject when in contactwith the acoustic coupling component; a signal generation and processingdevice in communication with the acoustic probe device and structured toinclude (i) a transmit and receive electronics (TRE) unit, and (ii) adata processing unit including a memory to store data and a processorcoupled to the memory to process data, in which the TRE unit includes awaveform generator in communication with the data processing unit andone or more waveform synthesizers in communication with the waveformgenerator to generate one or more waveforms according to waveforminformation provided by the data processing unit via the waveformgenerator, in which the transmittable acoustic waveforms correspond tothe one or more waveforms generated by the signal generation andprocessing device; and a position tracking device in communication withthe signal generation and processing device and operable to track theposition of the transducer elements of the acoustic probe device, inwhich the data processing unit is operable to process the receivedreturned acoustic waveforms to produce a data set including theinformation from the at least part of the target volume, the informationincluding at least one of location coordinates, orientation, or motionof the orthopedic structure of the body part with 6DoF.

Example 2 includes the system of example 1, in which the data processingunit is in communication with a surgical system and operable to transferthe produced data set to the surgical system such that the surgicalsystem can perform an operation or procedure on the orthopedic structurebased on the information contained in the data set.

Example 3 includes the system of example 1, in which the positiontracking device includes an optical sensor including one or more of acamera, an image sensor including a charge-coupled device (CCD), or alight emitting diode (LED).

Example 4 includes the system of example 1, in which the acousticcoupling component includes a hydrogel including one or morepolymerizable materials that form a network structured to entrap anaqueous fluid inside the hydrogel, in which the hydrogel is structuredto conform to an outer surface of the body part and the transducerelements, in which, when the acoustic coupling component is in contactwith the outer surface of the body part, the acoustic coupling componentprovides an acoustic impedance matching between the receiving medium andthe acoustic signal transducer elements.

Example 5 includes the system of example 4, in which the hydrogel isstructured to conform to the body part in complete contact with thesurface, without packets of air or voids formed between acousticcoupling component and the body part.

Example 6 includes the system of example 1, in which the TRE unitincludes an array of analog to digital (A/D) converters to convert thereceived returned acoustic waveforms received by the array of transducerelements of the acoustic probe device from analog format to digitalformat as a received waveform that includes information of at least partof the target volume, one or more amplifiers in communication with theone or more waveform synthesizers to modify the waveforms provided tothe acoustic probe device for transmission, and one or morepre-amplifiers in communication with the acoustic probe device and thearray of A/D converters to modify the received returned acousticwaveforms provided to the A/D converters.

Example 7 includes the system of example 1, in which the acoustic probedevice includes a signal interface module connectable to the TRE unit ofthe signal generation and processing device, the signal interface moduleincluding a multiplexing unit in communication with the array oftransducer elements to select one or more transducing elements of thearray to transduce the waveforms into the corresponding acousticwaveforms, and to select one or more transducing elements of the arrayto receive the returned acoustic waveforms.

Example 8 includes the system of example 1, in which the signalgeneration and processing device is operable to generate arbitrarywaveforms, in which the arbitrary waveforms include an arbitrarywaveform describable mathematically.

Example 9 includes the system of example 8, in which the arbitrarywaveforms include one or more of rectangular pulses, triangular pulses,impulse pulses, Gaussian pulses, sinusoidal pulses, sinc pulses, Mexicanhat wavelet pulses, Haar wavelet pulses, linear FM chirped pulses,hyperbolic FM chirped pulses, coded pulses, binary coded pulses, ternarycoded pulses, phase coded pulses, complementary binary coded pulses,amplitude coded pulses, phase and amplitude coded pulses, frequencycoded pulses, stepped sine wave pulses, shaped spectrum pulses, orcombinations thereof.

Example 10 includes the system of example 8, in which the signalgeneration and processing device is operable to arbitrarily delay,apodize, steer and beamform the arbitrary waveforms.

Example 11 includes the system of example 1, in which the signalgeneration and processing device is operable to generate a compositewaveform including two or more of individual orthogonal coded waveformscorresponding to one or more frequency bands that are generated by theone or more waveform synthesizers according to the waveform information,in which the individual orthogonal coded waveforms are mutuallyorthogonal to each other and correspond to different frequency bands,such that each of the individual orthogonal coded waveforms includes aunique frequency with a corresponding phase.

Example 12 includes the system of example 11, in which each of theindividual orthogonal coded waveforms includes a plurality of amplitudesand a plurality of phases that are individually amplitude weighted andindividually phase weighted, respectively.

Example 13 includes the system of example 11, in which the signalgeneration and processing device is operable to determine a frequencyband, an amplitude, a time-bandwidth product parameter, and a phaseparameter of each individual orthogonal coded waveform.

Example 14 includes the system of example 13, in which the phaseparameter is determined from a set of a pseudo-random numbers or from aset of deterministic numbers.

Example 15 includes the system of example 1, in which the target volumeincludes a tissue structure of the biological subject, and the shapedsection of the probe device is in contact with the body part of thebiological subject.

Example 16 includes the system of example 15, in which the body partincludes an abdomen, a thorax, a neck including the throat, an arm, aleg, a knee joint, a hip joint, an ankle joint, an elbow joint, ashoulder joint, a wrist joint, a breast, a genital, or a head includingthe cranium.

Example 17 includes the system of example 15, in which the biologicalstructure includes a cancerous or noncancerous tumor, an internallegion, a connective tissue sprain, a tissue tear, or a bone.

In one example of the present technology (example 18), a method forproducing orthopedic data using acoustic waveforms includes transmittingacoustic signals from a plurality of acoustic transducer elements in anarray of an acoustic probe device toward a target volume of anorthopedic structure of a body part of a biological subject to which theacoustic probe device is in contact; receiving acoustic echoes thatreturn from at least part of the target volume at one or more of thetransducer elements, in which the received acoustic echoes include atleast some waveform components corresponding to the transmitted acousticsignals; determining positions of the acoustic transducer elements ofthe acoustic probe device during the transmitting of the acousticsignals and the receiving of the acoustic echoes; processing thereceived acoustic echoes to produce spatial information corresponding toreturned acoustic echoes from the orthopedic structure including one orboth of soft tissue and bone, in which the processing includesdetermining an echo signature including unique specular pattern dataassociated with the acoustic echoes returned from a tissue-boneinterface of the orthopedic structure; and determining a location or anorientation, or both, of the orthopedic structure in a 6DoF coordinatespace based on the spatial information from the orthopedic structure byquantitatively comparing to sample patterns using the determinedpositions of the acoustic transducer elements.

Example 19 includes the method of example 18, including determiningtopography of the bone of the orthopedic structure in a 6DoF coordinatespace based on the spatial information from the orthopedic structure byquantitatively comparing to sample patterns using the determinedpositions of the acoustic transducer elements.

Example 20 includes the method of example 18, in which the determiningthe positions of the acoustic transducer elements includes determininglocation of the transducer elements relative to a fixed point in threedimensional space.

Example 21 includes the method of example 18, in which the transmittingthe acoustic signals includes transmitting sequentially one-at-a-time,simultaneously, or in a time-staggered or time-delayed pattern.

Example 22 includes the method of example 18, in which the processingthe received returned acoustic waveforms includes amplifying, filtering,and digitally sampling the acoustic echoes corresponding to the spatialinformation from the soft tissue and the bone of the orthopedicstructure; and storing the spatial information as data.

Example 23 includes the method of example 18, in which the uniquespecular pattern data includes cross-sectional patterns over a length ofthe bone for the sampled spatial information.

Example 24 includes the method of example 18, in which the producedspatial information includes spectral information corresponding to theacoustic echoes from the orthopedic structure.

Example 25 includes the method of example 18, further includingproviding the location and/or orientation of the orthopedic structure ina data set to a surgical system operable to perform an operation orprocedure on the orthopedic structure based on the information containedin the data set.

Example 26 includes the method of example 25, in which the providing thedata set to the surgical system includes transferring the data set tothe surgical procedure in real time during implementations of the methodinclude the transmitting of the acoustic signals and the receiving ofthe acoustic echoes into and out of the biological subject during theoperation or procedure by the surgical system.

In one example of the present technology (example 27), an acousticorthopedic tracking device includes an acoustic probe including asupport frame having a curved shape to interface a body part of abiological subject, and an array of transducer elements arranged on thecurved support frame and operable to transmit acoustic waveforms towarda target volume of an orthopedic structure in the body part and toreceive acoustic echoes that return from at least part of the targetvolume of the orthopedic structure; an acoustic coupling medium coupledto the array of transducer elements and operable to conduct the acousticwaveforms between the transducer elements and the body part of thebiological subject when in contact with the acoustic coupling medium,and a signal generation and processing unit in communication with thetransducer elements and structured to include a housing, a transmit andreceive electronics (TRE) unit disposed in the housing, and a dataprocessing unit disposed in the housing and including a memory to storedata and a processor coupled to the memory to process data, in which theTRE unit includes a waveform generator in communication with the dataprocessing unit and one or more waveform synthesizers in communicationwith the waveform generator to generate one or more waveforms accordingto waveform information provided by the data processing unit via thewaveform generator, in which the acoustic waveforms correspond to theone or more waveforms generated by the signal generation and processingunit, and the returned acoustic echoes include at least some waveformcomponents corresponding to the transmitted acoustic waveforms, and inwhich the data processing unit is configured to process the returnedacoustic echoes to produce spatial information corresponding to theacoustic echoes from the orthopedic structure including one or both ofsoft tissue and bone by identifying specular pattern data associatedwith the acoustic echoes returned from a tissue-bone interface of theorthopedic structure, and to determine a location or an orientation, orboth, of the orthopedic structure in a 6DoF coordinate space based onthe spatial information from the orthopedic structure by quantitativelycomparing to sample patterns using positional data of the transducerelements during transmit and receive operations of the acoustic probe.

Example 28 includes the device of example 27, in which the signalgeneration and processing unit is operable to receive the positionaldata from a position tracking device in communication with the signalgeneration and processing unit to track the position of the transducerelements of the acoustic probe device during the transmit and receiveoperations of the acoustic probe.

Example 29 includes the device of example 27, in which the dataprocessing unit is operable to generate a data set including thedetermined location, orientation, or location and orientation of theorthopedic structure of the body part in the 6DoF coordinate space.

Example 30 includes the device of example 29, in which the dataprocessing unit is in communication with a surgical system and operableto transfer the produced data set to the surgical system such that thesurgical system can perform an operation or procedure on the orthopedicstructure based on the information contained in the data set.

Example 31 includes the device of example 27, in which the acousticcoupling medium includes a hydrogel including one or more polymerizablematerials that form a network structured to entrap an aqueous fluidinside the hydrogel, in which the hydrogel is structured to conform toan outer surface of the body part and the transducer elements, in which,when the acoustic coupling medium is in contact with the outer surfaceof the body part, the acoustic coupling medium provides an acousticimpedance matching between the body part and the acoustic signaltransducer elements.

Example 32 includes the device of example 27, in which the TRE unitincludes an array of analog to digital (A/D) converters to convert thereturned acoustic echoes received by the array of transducer elementsfrom analog format to digital format as a received waveform thatincludes information of at least part of the target volume, one or moreamplifiers in communication with the one or more waveform synthesizersto modify the waveforms provided to the acoustic probe for transmission,and one or more pre-amplifiers in communication with the acoustic probeand the array of A/D converters to modify the returned acoustic echoesprovided to the A/D converters.

Example 33 includes the device of example 27, in which the acousticprobe includes a signal interface module connectable to the TRE unit ofthe signal generation and processing unit, the signal interface moduleincluding a multiplexing unit in communication with the array oftransducer elements to select one or more transducing elements of thearray to transduce the waveforms into the corresponding acousticwaveforms, and to select one or more transducing elements of the arrayto receive the returned acoustic echoes.

Example 34 includes the device of example 27, in which the signalgeneration and processing unit is operable to generate arbitrarywaveforms, in which the arbitrary waveforms include an arbitrarywaveform describable mathematically.

Example 35 includes the device of example 34, in which the arbitrarywaveforms include one or more of rectangular pulses, triangular pulses,impulse pulses. Gaussian pulses, sinusoidal pulses, sinc pulses, Mexicanhat wavelet pulses, Haar wavelet pulses, linear FM chirped pulses,hyperbolic FM chirped pulses, coded pulses, binary coded pulses, ternarycoded pulses, phase coded pulses, complementary binary coded pulses,amplitude coded pulses, phase and amplitude coded pulses, frequencycoded pulses, stepped sine wave pulses, shaped spectrum pulses, orcombinations thereof.

Example 36 includes the device of example 34, in which the signalgeneration and processing unit is operable to beamform and steer thearbitrary waveforms.

Example 37 includes the device of example 27, in which the signalgeneration and processing unit is operable to generate a compositewaveform including two or more of individual orthogonal coded waveformscorresponding to one or more frequency bands that are generated by theone or more waveform synthesizers according to the waveform information,in which the individual orthogonal coded waveforms are mutuallyorthogonal to each other and correspond to different frequency bands,such that each of the individual orthogonal coded waveforms includes aunique frequency with a corresponding phase.

Example 38 includes the device of example 37, in which each of theindividual orthogonal coded waveforms includes a plurality of amplitudesand a plurality of phases that are individually amplitude weighted andindividually phase weighted, respectively.

Example 39 includes the device of example 37, in which the signalgeneration and processing unit is operable to determine a frequencyband, an amplitude, a time-bandwidth product parameter, and a phaseparameter of each individual orthogonal coded waveform.

Example 40 includes the device of example 39, in which the phaseparameter is determined from a set of a pseudo-random numbers or from aset of deterministic numbers.

Example 41 relates a tomographic array for use in an acoustic orthopedictracking system that includes a plurality of transducer elementsarranged to form a curved array configurable to be positioned around asubject of interest that includes both soft tissue and a target bone,each transducer element capable of both transmitting and receiving anacoustic wave, each transducer element having a height, a width andbeing positioned at a distance from a neighboring element. Thetomographic array also includes an acoustic coupler that forms anacoustic signal transmission interface between the plurality oftransducer elements and the subject of interest.

Example 42 relates to configuration in which each transducer element isindependently addressable to either transmit or receive an acousticsignal to or from the subject of interest.

Example 43 relates to a configuration in which the tomographic array isoperable with an acoustic wave including a particular wavelength, andeach transducer element is positioned at a distance from a neighboringelement in a range 0.5 to 2 times the particular wavelength. In thisexample, the acoustic wave can include a range of wavelengths, and thedistance between the neighboring elements can be selected to be in therange 0.5 to 2 times a wavelength that is selected or chosen from therange of wavelengths.

Example 44 relates to a configuration in which the tomographic array isconfigured to allow a contiguous first set of the transducer elements tobe energized for transmission of a first acoustic signal.

Example 45 relates to a configuration in which a focal point of theacoustic signal is positioned within a sector subtended by an arc lengthand an angle spanned by the contiguous first set of the transducerelements.

Example 46 relates to a configuration in which the tomographic array isconfigured to allow a contiguous second set of the plurality oftransducer elements to be energized for transmission of a secondacoustic signal.

Example 47 relates to a configuration in which the first set and thesecond set have at least one transducer element in common.

Example 48 relates to a configuration in which the tomographic array isconfigured to include a receive aperture that includes a first set oftransducer elements from the plurality of transducer elements, and atransmit aperture that includes a second set of transducer elements fromthe plurality of transducer elements, where the receive aperture isequal to or larger than the transmit aperture and the transmit apertureis positioned entirely within the receive aperture.

Example 49 relates to a configuration in which the tomographic array isconfigured to include a first and a second aperture positioned withinthe tomographic array to include non-overlapping transducer elements,each aperture capable of both receiving and transmitting an acousticsignal, and the first aperture includes a first number of transducerelements, the second aperture includes a second number of transducerelements, the first number and the second number having been selected tomaintain the same f-number at a surface of the subject of interest(e.g., a target bone) for each of the first and the second aperture.

Example 50 relates to a configuration in which the tomographic array isconfigured to a first transmit aperture and a first receive aperture,and wherein the first receive aperture is positioned between 90 degreesand −90 degrees away from a phase center of the first transmit aperture.

Example 51 relates to a method for transmitting and receiving anacoustic signal in an imaging system that includes a plurality oftransducer elements arranged to form a curved array configurable to bepositioned around a subject of interest that includes both soft tissueand a target bone. Such method includes energizing a first set oftransducer elements that form a transmit aperture for transmitting theacoustic signal to the subject of interest, receiving at a second set oftransducer elements that form a receive aperture receiving at least aportion of the transmitted acoustic signal after interaction with thesubject of interest. The first set of transducer elements includes atleast one transducer element, and the second set of transducer elementsincludes a plurality of contiguous transducer elements each separatedfrom a neighboring transducer element by a distance without anintervening transducer element.

Example 52 relates to energizing the first set of transducer elementsthat includes forming a first acoustic signal having a focal point thatis positioned within a sector subtended by an arc length and an anglespanned by a plurality of transducer elements within the first set oftransducer elements.

Example 53 relates to forming a second acoustic signal using a third setof transducer elements that has at least one transducer element incommon with the first set.

Example 54 relates to a scenario in which the receive aperture is equalto or larger than the transmit aperture and the transmit aperture ispositioned entirely within the receive aperture on an arc formed by theplurality of transducer elements.

Example 55 relates to a scenario in which the first set and the secondset of transducer elements have no transducer elements in common, thefirst set and the second set of transducer elements each operate aseither the receive aperture or as the transmit aperture, and the firstset and the second set of transducer elements are selected to maintainthe same f-number at a surface of the subject of interest (e.g., atarget bone) for apertures formed by the first and the second set oftransducer elements.

Example 56 includes energizing a third set of transducer elements totransmit another acoustic signal and receiving at least a portion of anacoustic signal that is produced due to interaction of the acousticsignal produced by the third set of transducer elements with the subjectof interest.

Example 57 includes iteratively energizing different sets of transducerelements and receiving acoustic signals produced as a result ofinteraction of acoustic waves with the subject of interest until all ofthe plurality of transducer elements have been energized at least once.

Example 58 relates to a scenario in which, in each iteration, differentsets of transducer elements are selected in a random selection pattern.

Example 59 relates to a scenario in which, in each iteration, differentsets of contiguous transducer elements are selected.

Example 60 relates to a scenario in which, in each iteration, differentsets of non-contiguous transducer elements are selected.

Example 61 relates to a scenario in which each iteration includestransmission of two or more acoustic signals that are separated in timefrom one another, followed by reception of two or more acoustic signalsthat are separated in time.

Example 62 includes the device of example 43 that comprises one transmitchannel addressable to all transducer elements and one receive channeladdressable to all transducer elements.

Example 63 relates to example 62 in which the transmit element isselected from the plurality of elements and the receive element isselected to be the same as the transmit element for a giventransmission.

Example 64 includes the device of example 43 that comprises one transmitchannel addressable to all transducer elements and two receive channelsaddressable to all transducer elements.

Example 65 relates to example 64 in which the transmit element isselected from the plurality of transducer elements and one receiveelement is selected to be the same as the transmit element for a giventransmission and the second receive element is selected to be aneighboring element with no elements in between.

Example 66 relates to example 64 in which the transducer elements aresuccessively indexed and one receive channel is addressable to eventransducer element indices and the other receive channel is addressableto odd transducer element indices.

Specific Example of an OTS System

The disclosed acoustic orthopedic tracking system (OTS) can be used toaugment a surgical system, e.g., such as a robotic arm for interactiveorthopedic surgery, by providing accurate, timely, 6DoF bone positionsbefore and during orthopedic surgical operations. The disclosed acousticOTS technology can provide non-imaging data (e.g., range Dopplermeasurement), and can additionally or alternatively provide imagingdata. It is envisioned that, due to the advantages proffered by thedisclosed acoustic OTS, the disclosed system will replace, at least inpart, current tracking systems which typically utilizes LEDelectro-optical trackers pinned to the patient's femur and tibia.

In some implementations, the disclosed acoustic OTS can provide a thirdparty surgical navigation system (3PSNS) with relative positional dataintra-operatively for human femur and tibia bone targets. This exampleimplementation of the disclosed acoustic OTS is applicable to humanfemur and tibia bones, and the system is also engineered to characterizeother orthopedic anatomical features and structures, e.g., adaptation toother human or animal bone targets.

In some embodiments, for example, the disclosed acoustic OTS includes anarray of ultrasound transducers at locations and angular positions thatcan transmit and receive ultrasound signal data and be concurrentlytracked by a 3D position tracking system, e.g., such as anelectro-optical SNS. Positional data can be referenced to a coordinatesystem that is registered to 3D models of the bones to be tracked forrobotic assisted orthopedic surgeries. In some implementations, forexample, the 3D bone models can be prepared prior to the surgicaloperation by CT scan or other 3D imaging modality as part of thesurgical planning process.

FIG. 9 shows the disclosed acoustic OTS system integrated with example3PSNS system components. In the example shown in FIG. 9, the exemplaryOTS Ultrasound transducer arrays are attached to the patient's externalleg skin surfaces to monitor the position of the patient's bones. TheOTS provides positional and angular reference data to the exampleelectro-optical SNS allowing the 3PSNS to determine the position of the3PSNS optical arrays with respect to the patient's bone coordinatesystem.

FIG. 10A shows the relationship between the patient's bone coordinatesystem (x₁, y₁, z₁), the example OTS ultrasound transducer arraycoordinate system (x₂, y₂ and z₂) and the example 3PSNS optical arraycoordinate system (x₃, y₃ and z₃) at time t=0, when the OTS acquires thearbitrary point, P, and its associated coordinate system (x₁, y₁, z₁).

For example, with the SNS optical array knowing the relative position ofthe reference point, P, with respect to the SNS frame of reference, theSNS can register the positional relationship between point P and the“known” navigational points, Q, of the patient's bone surface.

Using a software 3D solid model of the bone prepared from CT scan data,for example, the received ultrasound signals are matched to the bonemodel to continuously determine the positional relationship of OTSultrasound array coordinate system (x′₂, y′₂, z′₂) to the bonecoordinate system (x₁, y₁, z₁) at any future time t=T after initialacquisition. As the array is not fixed to the patient's bone, anymovement of the array relative to the bone is measured and reported tothe 3PSNS system as a relative position (x′₂, y′₂, z′₂) includingangular changes for full 6DoF tracking, as illustrated in FIG. 10B. FIG.10B shows a diagram depicting a bone tracking coordinate system showingultrasound array displacement at future time t=T.

The example acoustic OTS provides both translational data ΔR₁₂(T), plustransducer coordinate rotational information as 3×3 directional cosinematrix elements, or in any other mutually agreed format, for thetransducer array coordinate system (x′₂, y′₂, z′₂) for all sample times,T, after acquisition. If for any reason a “track lost” condition occurs,the OTS will go in an acquisition mode to reacquire the original virtualReference Point, P, and associated coordinate system and set a digital“track lost” flag. In some implementations, for example, the onlyanticipated condition where the OTS would not automatically reacquirepoint P would be if the OTS Transducer Array for some reason becamedetached from the patient's skin.

An example hardware block diagram for the OTS is shown in FIG. 11. Insome embodiments of the system, for example, the OTS hardware subsystemscan include the following elements: Ultrasound Transducer Arrays #1 and#2: transmit and receive ultrasound signals reflected from the bonesurfaces; Tx/Rx Electronics: include the ultrasound Transmittercircuitry and Receiver preamplifiers and A/D converters. RF signals aretransferred to and from the transducer arrays. The received signals aredigitized, filtered and fed into the real time processor.

Real-time Data Processor: a block diagram of an example OTS softwarearchitecture is shown in FIG. 12.

System Operations: The following sections are described as an example ofa system of the present technology's operational modes, parameters, andprocedures. Other operational modes, parameters, and procedures may alsobe implemented using the system of the present technology.

Example Modes

Setup Mode: Setup mode allows a 3rd party host system operator to load3D bone solid models, and to perform other maintenance tasks includingarray calibration. Setup mode can be the default mode when 3D solidmodels have not yet been loaded into the system.

Self-test Mode: Self-test may be programmed to automatically test majorhardware functions including arrays, Tx/Rx functions, processor and UOinterfaces. Self-test returns a pass/fail indication including adetailed status message containing the results of each test performed.Status messages are transmitted to either the host system or an attachedconsole, if used, for maintenance.

Manual Test Mode: Manual test allows an operator to perform each oftests performed in self-test individually and obtain lower-level statusinformation for troubleshooting. Manual test can be programmed toprovide measurement data that can be observed from a test dashboard thatincludes charts showing the returned signals from each of the transducerelements as well as 6DoF data in a numeric or graphical format.

Run Mode: The Run mode includes two sub-modes; Acquire and Track, whichare described as follows.

Acquire Mode: When commanded to the Run mode, the example acoustic OTSwill begin the Acquire sub-mode, whereby it is searching for a bonecross-section match to the 3D solid model and thus not yet providingvalid positional data to the STS. During this mode, messages will becontinuously sent to the STS, e.g., via the IEEE 1394 interface,indicating current mode and health status of the acoustic OTS. When theacoustic OTS determines it has an acceptable match to the solid model,the Acquire Mode is completed and the OTS is registered to the 3D solidmodel.

Track Mode: Once the OTS software determines a sufficient match to the3D solid model, it automatically transitions to Track mode and beginsreporting 6DoF positional data to the STS via the IEEE 1394 serialinterface. The message stream includes a health status word with eachframe indicating the validity of the measurement of the of the bonepositions relative to the arrays. This message may include an errorestimate based on correlation of the received ultrasound signals withthe 3D reference models. If for any reason the OTS software senses abone cross-section that does not adequately match the 3D solid model, itwill automatically return to the Acquire mode and re-register the OTS tothe 3D solid model.

Array and Mode Selection and Array Identification: The acoustic OTS canbe programmed to automatically detect the type of array(s) connected tothe system. Codes for the detected array type can be included in thestatus messages sent to the host system.

System or Subsystem Functional Operational Parameters

6DoF Tracking: The acoustic OTS can be programmed to be used as asubsystem of a 3PSNS system to provide for 6DoF tracking of ultrasoundtransducer arrays with respect to predefined coordinate systemsregistered to patients' bones for robotic assisted orthopedic surgery.

6DOF Tracking Sample Frequency: The acoustic OTS tracking samplefrequency can be programmed to be 1 kHz or more.

6DoF Tracking Latency: The acoustic OTS tracking latency can beprogrammed to be less than 3 ms.

6DoF Tracking Latency Jitter: The acoustic OTS tracking latency jittercan be programmed to be not more than a negligible amount.

Relative Target Tracking Speed: The acoustic OTS can be programmed totrack relative position of the transducer array with respect to the boneat linear speeds up to 50 mm/s.

Target Tracking Range: The acoustic OTS can be programmed to trackrelative position of the transducer array with respect to the bone overa range of movement +/−25 mm from the initialized starting position.

Anatomical Targets: The acoustic OTS can be programmed to be capable oftracking transducer array positions with respect to the followinganatomical targets, for example, Human femur and Human tibia.

Human Patient Population: The OTS can support orthopedic surgeryprocedures on male and female human patients between 5th and 95thpercentile calf and mid-thigh dimensions as specified in Table 1 below.

TABLE 1 Human Patient Population Characteristics Minimum Maximum PatientParameter (5^(th) Percentile) (95^(th) Percentile) Age, years Over 20Sex male and female Calf Circumference¹, cm 29.8 48.0 Mid-ThighCircumference¹, cm 38.2 75.0 Weight¹, lb 102 275

The OTS system may be used on patients younger than age 20 if theirlimbs are within the size range specified in Table 1.

6DoF Data Output Parameters: The OTS is able to output 6DoF position andangle parameters, e.g., such as those defined in Table 2 below.

TABLE 2 6DoF Parameters Parameter Definition Units Range CoordinateTranslation Origin O′₂ Position with respect to O₂ at time sample T ΔX₂x₂•ΔR₁₂ meters −1 to 1 ΔY₂ y₂•ΔR₁₂ meters −1 to 1 ΔZ₂ z₂•ΔR₁₂ meters −1to 1 Coordinate Rotation O′₂ Coordinate Rotation with respect to O₂ attime sample T cos (θ₁₁) x₂•x′₂ unitless −1 to +1 cos (θ₁₂) x₂•y′₂unitless −1 to +1 cos (θ₁₃) x₂•z′₂ unitless −1 to +1 cos (θ₂₁) y₂•x′₂unitless −1 to +1 cos (θ₂₂) y₂•y′₂ unitless −1 to +1 cos (θ₂₃) y₂•z′₂unitless −1 to +1 cos (θ₃₁) z₂•x′₂ unitless −1 to +1 cos (θ₃₂) z₂•y′₂unitless −1 to +1 cos (θ₃₃) z₂•x′₂ unitless −1 to +1

Where x₂ is the unit vector in X₂ direction, and x′₂ is the unit vectorin X′₂ direction, etc., and cos(θ_(ij)) are the elements of thedirection cosine matrix describing the angular movement of thetransducer array at time T as illustrated in the equation (A) below andshown in FIG. 13.

$\begin{matrix}{\begin{pmatrix}X_{2}^{\prime} \\Y_{2}^{\prime} \\Z_{2}^{\prime}\end{pmatrix} = {\begin{pmatrix}{\cos \left( \theta_{11} \right)} & {\cos \left( \theta_{12} \right)} & {\cos \left( \theta_{13} \right)} \\{\cos \left( \theta_{21} \right)} & {\cos \left( \theta_{22} \right)} & {\cos \left( \theta_{23} \right)} \\{\cos \left( \theta_{31} \right)} & {\cos \left( \theta_{32} \right)} & {\cos \left( \theta_{33} \right)}\end{pmatrix}\begin{pmatrix}X_{2} \\Y_{2} \\Z_{2}\end{pmatrix}}} & (A)\end{matrix}$

In Equation (A) above, (X₂, Y₂, Z₂) is the OTS transducer coordinatereference at time t=0, when the system was initialized, and (X′₂, Y′₂,Z′₂) is the new transducer angular position due to the movement of thetransducer relative to the bone at a subsequent time t=T. Parameters x,y and z are measurements of the transducer's translation with respect tothe bone reference frame at time t=T. FIG. 13 shows a Femur 6DoFCoordinate System at Time T.

Operational Sequence: The acoustic OTS can be operated in the followingactivity sequence (e.g., knee arthroscopy, for example).

Example Pre-operative Planning: (1) Prepare 3D solid models of thepatient's femur and tibia from CT scan (or other 3D tomographic)imagery; (2) Assign an orthogonal right-hand sided reference frameregistered to point P on the 3D solid model (as shown in FIG. 13); (3)Verify/calibrate the OTS ultrasound arrays to appropriate 3D bonephantoms.

Example Day of Operation Planning: (1) Attach the acoustic OTStransducer arrays to patient thigh and calf at the appropriate distancesfrom the patella; (2) Activate the acoustic OTS system electronics andmonitor status including the TIB and MI output display indices via theexample 3PSNS console; (3) Initialize the OTS with the transducers intheir nominal positions to begin tracking via the example 3PSNS console;(4) Register the 3PSNS system to spatial fiducial points on theultrasound arrays; (5) Register the 3PSNS system with the acoustic OTSbone tracking to appropriate reference locations on the corticalsurfaces of the femur and tibia; (6) Proceed with robotic assistedorthopedic surgical procedure.

Transducer Arrays: The acoustic OTS transducer arrays can be configuredso that they are suitable for use over the range of anatomicaldimensions.

Femur Array(s)

Femur Array Position: The OTS femur array(s) can be configured so thatthey are able to map femur cortical surfaces between 6 and 12 cm fromthe knee joint.

Femur Array Scan Area: The OTS femur array(s) can be configured so thatthey are capable of scanning thigh areas between 35 and 75 cm incircumference (11.1 to 23.9 cm diameter).

Tibia Array(s)

Tibia Array Position: The OTS femur array(s) can be configured so thatthey are able to map tibia cortical surfaces between 6 and 12 cm fromthe knee joint.

Tibia Array Scan Area: The OTS femur array(s) can be configured so thatthey are capable of scanning calf areas between 28 and 48 cm incircumference (8.9 to 15.3 cm diameter).

Other Array(s): The disclosed technology can be used to implement arraysfor other human bones, e.g., such as the hip, spine and ankle.

Output Display Standard: The OTS ultrasound system can produce an outputin conformance with the Output Display Standard (NEMA UD 3-2004), as anFDA Track 3 device.

Bone Thermal Index: The OTS ultrasound system can be configured so thatit provides real-time reporting of the acoustic output bone thermalindex (TIB) at all times ultrasound is being transmitted. The TIB valueis an estimate of the number of degrees, C, temperature rise above theambient body temperature. TIB can be included in the data messagetransmitted to the 3PSNS.

Mechanical Index: The OTS ultrasound system can be configured so that itprovides real-time reporting of the acoustic output Mechanical Index(MI) at all times ultrasound is being transmitted. MI can be included inthe data messages transmitted to the 3PSNS.

Transducer Array Cleaning Materials: The OTS transducer arrays can beconfigured so that they are compatible with one or more of the followingcleaning materials, for example: 75% IPA, Cidex Plus 28 Day, Cidex OPA,Cidezyme, Klenzyme or Omnicide.

Implementations of the subject matter and the functional operationsdescribed in this patent document and attached appendices can beimplemented in various systems, digital electronic circuitry, or incomputer software, firmware, or hardware, including the structuresdisclosed in this specification and their structural equivalents, or incombinations of one or more of them. Implementations of the subjectmatter described in this specification can be implemented as one or morecomputer program products, i.e., one or more modules of computer programinstructions encoded on a tangible and non-transitory computer readablemedium for execution by, or to control the operation of, data processingapparatus. The computer readable medium can be a machine-readablestorage device, a machine-readable storage substrate, a memory device, acomposition of matter effecting a machine-readable propagated signal, ora combination of one or more of them. The term “data processingapparatus” encompasses all apparatus, devices, and machines forprocessing data, including by way of example a programmable processor, acomputer, or multiple processors or computers. The apparatus caninclude, in addition to hardware, code that creates an executionenvironment for the computer program in question, e.g., code thatconstitutes processor firmware, a protocol stack, a database managementsystem, an operating system, or a combination of one or more of them.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of nonvolatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices. The processor and the memory can be supplemented by, orincorporated in, special purpose logic circuitry.

While this patent document and attached appendices contain manyspecifics, these should not be construed as limitations on the scope ofany invention or of what may be claimed, but rather as descriptions offeatures that may be specific to particular embodiments of particularinventions. Certain features that are described in this patent documentand attached appendices in the context of separate embodiments can alsobe implemented in combination in a single embodiment. Conversely,various features that are described in the context of a singleembodiment can also be implemented in multiple embodiments separately orin any suitable subcombination. Moreover, although features may bedescribed above as acting in certain combinations and even initiallyclaimed as such, one or more features from a claimed combination can insome cases be excised from the combination, and the claimed combinationmay be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document and attached appendicesshould not be understood as requiring such separation in allembodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document and attachedappendices.

What is claimed is:
 1. A method for producing orthopedic data using acoustic waveforms, comprising: transmitting acoustic signals from a plurality of acoustic transducer elements in an array of an acoustic probe device toward a target volume of an orthopedic structure of a body part of a biological subject to which the acoustic probe device is in contact; receiving acoustic echoes that return from at least part of the target volume at one or more of the transducer elements, wherein the received acoustic echoes include at least some waveform components corresponding to the transmitted acoustic signals; determining positions of the acoustic transducer elements of the acoustic probe device during the transmitting of the acoustic signals and the receiving of the acoustic echoes; processing the received acoustic echoes to produce spatial information corresponding to returned acoustic echoes from the orthopedic structure including one or both of soft tissue and bone, wherein the processing includes determining an echo signature including unique specular pattern data associated with the acoustic echoes returned from a tissue-bone interface of the orthopedic structure; and determining a location or an orientation, or both, of the orthopedic structure in a six degrees of freedom (6DoF) coordinate space based on the spatial information from the orthopedic structure by quantitatively comparing to sample patterns using the determined positions of the acoustic transducer elements.
 2. The method of claim 1, comprising: determining topography of the bone of the orthopedic structure in a six degrees of freedom (6DoF) coordinate space based on the spatial information from the orthopedic structure by quantitatively comparing to sample patterns using the determined positions of the acoustic transducer elements.
 3. The method of claim 1, wherein the determining the positions of the acoustic transducer elements includes determining location of the transducer elements relative to a fixed point in three dimensional space.
 4. The method of claim 1, wherein the transmitting the acoustic signals includes transmitting sequentially one-at-a-time, simultaneously, or in a time-staggered or time-delayed pattern.
 5. The method of claim 1, wherein the processing the received acoustic echoes includes amplifying, filtering, and digitally sampling the acoustic echoes corresponding to the spatial information from the soft tissue and the bone of the orthopedic structure; and storing the spatial information as data.
 6. The method of claim 1, wherein the unique specular pattern data includes cross-sectional patterns over a length of the bone for the sampled spatial information.
 7. The method of claim 1, wherein the produced spatial information includes spectral information corresponding to the acoustic echoes from the orthopedic structure.
 8. The method of claim 1, further comprising: providing the location and/or orientation of the orthopedic structure in a data set to a surgical system operable to perform an operation or procedure on the orthopedic structure based on the information contained in the data set.
 9. The method of claim 8, wherein the providing the data set to the surgical system includes transferring the data set to the surgical procedure in real time during implementations of the method include the transmitting of the acoustic signals and the receiving of the acoustic echoes into and out of the biological subject during the operation or procedure by the surgical system. 